Kathleen "Kat" Moon (née Slater) arrived in Albert Square in 2000 and she is the daughter of Charlie Slater and Viv Slater as well as the mother of Zoe and Luke Slater and Tommy, Bert and Ernie Moon. Kat is the typical Slater, bad tempered and always says what's on her mind, much like her younger cousin Stacey Slater.
Born in 1970 to Charlie Slater and Viv Slater. One day, when Kat was a young girl, she was sick, and she couldn't go to school. Viv was busy, so Kat ended up going to work with Charlie in his cab. Kat sat in the passenger side on a seat made out of pillows and Charlie wrapped her in a blanket, and they drove around all day picking' up fares. They went over the Thames, through the tunnel, singing songs, laughing and talking. After that day Kat tried to pretend she was sick all the time but her mum Viv got suspicious. A few years later Kat went out in Charlie's cab again, but it wasn't the same. She got bored. Charlie got irritable, and they just argued When Kat was 15 her mother Viv took Kat's sisters Belinda, Little Mo and Zoe to Ireland on Holiday. Kat didn't want to go so she stayed home with her father Charlie and sister Lynne. She took them in there in a van, and one day she drove them into a village and left them in a playground. Val went to a Church to pray. When Val finished, and she came out she was crying, and Belinda asked her what was wrong. Val said its all Kat's fault. As there were driving away in the van, Belinda turned and looked back at the church, and these two people were staring at us, watching us go. One of them was holding a little boy who may have been Kat's son Luke Slater, Belinda remembered the name of the village as Red Water.
When Kat’s ‘sister‘, Zoe, planned to leave London to work with their uncle, Harry Slater, in Spain, she shouted down Kat’s objections with ‘You can’t tell me what to do, you ain’t my mother.’, to which Kat replied ‘Yes, I am!‘ The story was revealed that Harry had sexually abused her, getting her pregnant at the age of thirteen. Her father Charlie Slater, Harry’s brother, was unaware of this, assuming that the father was a boy with whom Kat attended school. He and his late wife Viv raised Zoe as their daughter together.
The woman Zoe had called her mother was really her grandmother, her ‘dad’ was really her uncle and her grandfather; her 'grandmother' was really her great-grandmother; her ‘sister’ was really her mother, her three other 'sisters' were really her aunts and her cousins, and her ‘uncle’ was really her great-uncle and her father! Zoe fled Albert Square, and Kat, insulted by Harry, attempts suicide but is found in the park by Zoe and is rushed to hospital. Charlie attacked and disowned Harry, and ordered him to leave Albert Square and never return. One of Kat’s boyfriends was Dr. Anthony Trueman. He was mesmerized by her, and they had a lot of fun, but Kat ditched him when he told her he was falling in love with her. Her daughter, Zoe, later became engaged to Anthony, much to the disapproval of Kat and the rest of the Slater family. Zoe cut all ties with Kat over this. As the wedding approached, Zoe disappeared saying, when she reappeared, that she had needed to get away and think about the serious step she was about to take. She was devastated to find Anthony and Kat were back together, this time in a more serious relationship. Kat realized Anthony’s doctor and ‘posh’ friends looked down on her, and that she and Anthony would never fit together, and they broke up. Kat later discovered she was pregnant with Anthony’s baby. She thought about having an abortion but decided to keep the baby. Unfortunately, she had a miscarriage and was comforted by Alfie Moon. It was very sad for her!
In September 2010, Kat returned to the Square, being heavily pregnant, although she tried to hide this at first from her husband, Alfie. However, she soon revealed to him that the baby was not his but Michael Moon's baby - Alfie's second cousin. Kat eventually gave birth on the 31st December 2010 - at the same time as Ronnie Mitchell. But their happiness was short-lived when Ronnie's baby, James, died and a grieving Ronnie switched the babies, leading Kat to think her newborn baby was dead. Months later, Ronnie admitted her wrong-doing and the Moons were reunited with their son. In early 2012, Kat left Walford to live with Charlie, as he was very unwell, taking Tommy with her. Alfie was left in charge of the pub, and Roxy was kicked out of her house, so Alfie let Roxy work in the Vic and live with him. Eventually, Kat gave birth to a son she named Tommy.
Jean was having another breakdown as Michael had taken all of the Vic's money, £10,000. Kat and Alfie returned to find Jean in the bath. She confronted Alfie about it, but he denied he has it and that any of it ever happened. In Summer 2012 Kat began an affair with a mystery east-end local. In December 2012, Alfie discovered Kat's relationship was with one of the three Branning brothers. Devastated and furious with Kat, Alfie marched over to the Vic to find out which Branning it was. Kat later revealed she was having an affair with Derek. Alfie ended his relationship with Kat - leading her to spend Christmas at the Brannings with her secret lover, Derek.
Kat was reunited with Alfie after she had an affair in 2012. They then were forced to move out of the Vic by Phil (For Revenge) on Boxing Day, after Alfie jilted Roxy on their wedding day to be with Kat. On Christmas Day 2013, Kat revealed to Alfie that she was pregnant again. They spent their last day in the Vic with Mo, Charlie and Tommy happily together.
In February, Kat sees her cousin Stacey from a bus in London, on her way to visiting Alfie in a hotel. Over the coming weeks, Kat desperately tries to track Stacey down. When she does, she goes to Janine to ask her to drop the charges for accusing Stacey of stabbing her. Janine tells Kat she will lose the costs if she changed her alibithe night Michael died. In March at Janine's and Alice's trial, the truth comes out about Kat lying, so she is forced to do 100 hours of community service. Stacey is sent to prison after confessing she killed Archie. Kat gave birth to twin boys Bert and Ernie while visiting Jean in Hospital.
She then briefly moved back to the square, while her dad Charlie died from a heart attack and she became distraught. When the funeral day came, Kat was bitter toward Mo and Belinda had argued over Charlie with her. When Kat saw Stacey so crazed and wild, she decided to stay home for the funeral and aided Stacey, the twins and Stacey's newborn son, Arthur, all stay at the pub all day. Kat reminisced about many happy memories with her dad and his taxi; later when Stacey's husband returned from the church, Kat angrily confronted him, shouting at him for allowing Stacey to get so mentally unstable. When Belinda and Kat's grandmother are about to leave, Kat reconciled with Belinda and apologised for her wrongdoing and bitterness to her.
In March 2018, Lily Slater answers the door to an emotional Mo Harris, who has arrived back in the square to see Stacey and informed her that Kat, Stacey's cousin, has died but this was just a scam as she was in a lot of debt and therefore, she needed £5000. However, Stacey wasn’t aware that Mo was lying. Lily then notices that Stacey is upset and in her way to school, informed Martin, who becomes extremely worried about Stacey. Lily then finds a magazine full of pictures of coffins just as Stacey walks in the room and takes it off her. Stacey then breaks the news to Lily that Kat is dead and Lily becomes upset. A couple of days later, Lily answers the door to her grandmother Jean who tells Stacey and Mo that she just spoke to Kat on the phone and she isn't dead. Stacey then tells Jean that she couldn't have spoken to Kat because she is dead. Jay Brown then donates a coffin to Stacey and Lily puts her doll inside thinking it's a bed. Jean then explains to Lily that Kat will be buried in the ground and the coffin will be tightly closed, which makes Lily scared. During the Queen Vic, everyone tries to raise money for Kat's funeral, which is been hosted by Mick and Linda. Suddenly, Kat arrives in the Square and turned up at Stacey's door, just as Jean is putting Lily and Arthur to bed. Mo then explains that she lied about Kat's death for money and the Slaters become angry. Kat then turns up at the Vic with Mo, explaining what has happened and she then fakes a heart attack, which doesn't go to plan when people know she's faking. They then walk out of the Vic (now with everyone fighting) and return home to Jean, who is babysitting Lily, Arthur and Hope. After that, the Slaters become the most hated family on the Square but the hatred soon turns to Max when he returns to the square with his new wife Rainie and his granddaughter Abi. When Kat needs her washing done but has no money, she goes to see Martin and asks to use his washer to wash the kids' clothes and takes Lily along with her and tells Lily to act cute. Lily puts on a pet lip for Martin and he agrees to let them use his washer. He then pulls out one of Kat's tops and she tells him that it's Arthur's and he uses it for painting. Lily and Martin look at each other and laugh, especially when Martin pulls out a bra and says to Kat "I suppose this is Arthur's at all". Lily laughs and Kat tells Lily they’re going home but Martin tells Kat that Lily can stay with him for the day, which she does. After realising they are both still in love with each other, Martin and Stacey give their relationship another go and Martin moves back into the house.
It later reveals that Alfie is still in Spain with the kids after an incident that happened while Kat was looking after them. Kat had sex with a Spanish man upstairs and left the kids playing downstairs, Tommy boiled the kettle and water accidentally went on Bert. On the night of the Royal Wedding, Kat gives her cousin Hayley Slater a makeover, alongside Mo. Jean passes Hayley an umbrella on her way outside as Kat and Mo plan to tip dirty water on her. Hayley then goes out to confront them, and they stop. She then heads to a hotel room outside of Walford, where it reveals that Kat's husband Alfie Moon is the father of her unborn child, after having a one night stand. The pair talk and Alfie asks about Kat because Kat's children need to see her as Aflie is currently raising them after a fallout with Kat - which has made Kat refuse to even look at her boys.
Alfie tells Hayley he loves Kat but Hayley tells Alfie she thinks the baby is a girl and she could boss her big brothers around and Hayley will raise them as her own. However, Alfie replies by telling Hayley that Kat is the boys' mother, not her. Hayley gets mad and wants to have an abortion but Alfie tells her not to, but later, he changes his mind after Hayley talks him round. Alfie gives her the money and the next day Hayley makes an appointment at the hospital for a termination. Hayley then gets drunk and turns up late to her appointment, which makes them refuse to see her. She then makes a new one but changes her mind after Kat tells her she's a good person really. A few weeks later, Hayley is shocked when Stacey announces that her and Martin are back together and he will be moving back into the house. The Slaters then get an even bigger surprise when an envelope is put through the letter box saying Slaters. They all don't know if to open it or not and Hayley tells everyone that she is the only Slater. While pointing to Tiffany, Stacey, Mo and Jean, she arrogantly says "Fowler, Harris, Walters - oh and Bouchard" to prove a point that she should open the letter as she is the only Slater in the house. But Tiffany very sarcastically replies to Hayley saying "It's Butcher, actually".
Stacey opens the letter and to their surprise, it is the key's to Kat’s deceased father, Charlie Slater's old cab, with a note reading that Charlie’s friend had the cab and he promised Charlie that when he retired, he had to give the cab to the Slaters. Hayley tells Stacey she can fix it but she doesn't believe her, so Hayley goes to see fellow mechanic Keanu Taylor where she asks if there are any jobs. However, she didn't really want a job and was just trying to distract him, while she stole some tools to fix her Charlie's cab. Later on, she uses Tiffany's laptop so she can go online and see if anyone is interested in buying the cab. Tiffany spots her and this causes them to argue. Stacey pulls the pair apart but Tiffany goes to slap Hayley, which causes another fight to break out. Stacey pulls them apart once again and while Tiffany's back is turned, Hayley eats her toast - which makes Tiffany mad. Since the Slater family house is a bit over crowded, Martin gets annoyed with everyone. He then gets ready to go in the shower but realizes Tiffany is in. When Martin asks her is she is done, she replies "I’m washing my hair". Martin then comes downstairs and Tiffany comes out the shower, just as Mo runs up the stairs to use the bathroom. When the bathroom is finally free, Martin goes in the shower but is disturbed when Jean walks in. She then runs downstairs and Martin goes after her. Jean runs into the kitchen where everyone is and Martin explains what has just happened. Tiffany laughs, as does everyone but Jean says "to be fair Martin, I didn't see much". Everyone laughs again and Kat replies "Poor Stacey". Martin goes to turn away and Kat pulls down his towel, which is covering his body. Everyone screams and Tiffany covers her eyes but Stacey grabs the cloth and puts it over Tiffany's eyes. Martin goes upstairs to resume his shower and get ready. When he comes downstairs into the kitchen, he spots Lily on Tiffany's tablet and tells her she should play outside and get some air in her lungs because she looks pasty. A few minutes later, Lily comes downstairs tanned as Tiffany covered her in fake tan because Martin said she looked pasty. Martin then promises to take Lily to the doctor after he finishes work but later gets robbed. Lily overhears Martin talking to the rest of the family about it and decides to make her own movie, with the help of Hayley handing out the 'tickets'.
Jean then begins to take Stacey's children, Lily, Arthur and Hope to church, hoping to convince Lily to get christened. However once Jean confronts Stacey about this, Stacey disagrees. Jean then decides to see Martin and Kush to see how they would feel about having the children christened. She asks Kush if he would like to see Arthur christened but Kush replies, saying that he is a Muslim. Jean then asks Martin but he says that he isn't really religious and doesn't know how Stacey would feel about having Hope christened. Jean then mentions it to Stacey about having Lily christened and when Stacey asks Lily about this, she says she doesn't want to have one. Martin then begins to see how much a christening would mean to Jean after Jean confides in him that it would be the perfect idea for a big family gathering. Martin agrees as long as Jean manages to talk Stacey round. However, Stacey tells her that she has three kids and she won’t treat them differently, but Jean talks her round and eventually, Stacey agrees. Jean shows Stacey the dress she wore for her christening and she smiles. On the day of Hope's christening, Martin is drunk after a guys’ night out for his birthday with Kush and Robbie. The start of the day turns out to be a disaster when nobody can find Hope's christening dress. Stacey picks Kat as Hope’s godmother and Martin picks Robbie as her godfather. Kat then goes to a wall and tries to phone Alfie so she can talk to her kids. Hayley then discovers that Hope's christening dress is inside the towel on her head and takes it to the church. With Kat being missing, Stacey needs to decide on a godmother for Hope and suggests Mo but Martin says he doesn't want Mo to be a godmother to his daughter and everybody laughs. Tiffany then says she will do it but her cousin Bex Fowler says she is too young. The vicar then says that these decisions cannot be rushed just as Hayley walks in the room. Hayley is then forced to get Hope changed into her christening dress and Jean talks her round into becoming Hope's godmother. Hope is about to be christened when Kat walks in the room. Hayley then hands over Hope to Kat and walks off. Jean then goes after her and Hayley confides in her that she is pregnant. After that Hayley walks out the house and gets drunk - once again.
Jean then starts buying clothes for the baby, which gets Hayley mad as she doesn't want anyone finding out about her pregnancy. Soon, they agree to tell the whole family about the news. Hayley becomes friends with Kim Fox-Hubbard after they start going to parenting classes together. Stacey tells Hayley she can have Hope's old baby clothes, pram and her basket. Later, Hayley's mother Bev Slater arrives on the Square, promising Hayley that she is a changed woman and she came to see her because she found out she was pregnant. At first, Hayley is very optimistic and mad to find her mother in the Square. Soon, Hayley asks her mother to prove she has changed and the pair goes shopping together. After the shopping trip, they go to along to E20, only for Hayley to find out that her mother's intentions were to con money off the baby's father. The pair catfight and Hayley is just about to throw a glass in Bev's face. However, they are both thrown out by Billy Mitchell. Bev tells Hayley that she is just like her and the baby is going to end up just like Hayley. Bev then calls for a taxi and Hayley starts to bleed, but Bev smiles and says that Hayley should have got rid of the baby while she had the chance. She smiles and asks the taxi driver to pull away, as Hayley sits crying for her mother in the middle of the street. Hayley then goes into town and gets drunk.
In October, Jean sends Hayley to go shopping and get everything she needs for the baby’s arrival. Hayley becomes stressed in Honey Mitchell's shop when she can't figure out what size nappies to buy the baby. Honey tries to calm Hayley down just as Mariam Ahmed walks in. She tells Hayley to go home with her, and they chat. Mariam asks Hayley to look after her foster child Harley, while she finishes cooking. Hayley does this and stops him from crying. Hayley then walks into the living room and spots some pictures of a lot of children, whom Mariam and her partner Arshad have fostered in the past. Hayley places this one child who suffers from deformations due to his mother drinking while she was pregnant. Hayley tells Mariam how her and her mates used to make fun of this girl at school because she looked like that. Then Hayley becomes upset that her baby might have this as she drinks all the time during her pregnancy. She runs to home and confronts Jean about it. Jean tells Hayley that she isn't always drunk, well most of the time.
After a while, he goes to her house, making sure she got there safe but no one had seen her. Jean then says she knows where Hayley is and her and Kat go to Bev's old flat looking for Hayley as that is where she was brought up. They spot her sitting on the edge of the balcony with earphones in. Jean tells Kat she remembers which floor it was so they go up. Kat assumes Hayley is just relaxing, sitting on the edge but soon realizes that Hayley is about to commit suicide. Hayley continues to sit on the edge, listening to music and drinking her vodka. She tells her to stop being selfish and to get down but she doesn't listen and tells Kat she will really do it, just as she stands up with her arms out. Kat screams for Hayley to get back down, and she does, telling Kat that if she knew the truth, she would want her to do it. Jean intervenes and Hayley drops her vodka to ground, watching it smash into a million pieces. After a long time of trying, Jean eventually convinces Hayley to get down. The next day, a social worker arrives to speak to Hayley and tells her that she was brought up in care and just wants to help people. Hayley then tells her that she cancelled her abortion appointment and actually wanted to keep the baby. After the social worker leaves, Jean walks in and Hayley automatically blames her for calling social services. Jean denies it, just as Stacey and Kat walks in and Kat admits it was her not Jean. Hayley apologises to Jean and goes upstairs to pack her things to leave. Kat tells Stacey she was so close to jumping and needs help.
Two days before Halloween, Hayley tries to force herself into labour as she wants the baby to hurry up and be born. Originally, Hayley wants the baby to be put into care as she believes she’s just like her mother, who left Hayley all on her own for long periods of time at a young age. Hayley tries to eat some spicy food which Mariam gives her, but the baby kicks and she does not go into labour. She then decides to take a long walk through the Square but that doesn't help other. She is then spotted by Karen Taylor, Keanu's mother, who tells Hayley she should have sex and that, it’ll cause labour. Hayley then calls round Keanu, asking him to have sex with her. At first, Keanu is unsure about it, but thinks it would not be right. Eventually, Keanu agrees but tells Hayley that he is sweaty as he has just been for a run. He goes for a shower just as Kat, Jean and Mo walk in the house. Hayley manages to get rid of them and tells Keanu that it was a bad idea. Soon, Hayley's waters break and she decides to take herself to the hospital without telling anyone. Hayley begins to have contractions. Ian Beale asks for a lift to his meeting but Hayley screams at him and drops him off at the tube station, just before her telling him that if he doesn't get out, he will be delivering her baby. Hayley begins bleeding but people, such as Bernadette and Tiffany, think it’s a Halloween prank, not believing her and leaving her in pain. Hayley then decides to walk into an old house, where there are some teenagers who run away from her, also thinking it’s a prank. After being in labour for hours, Hayley eventually gives birth to a baby girl, early hours in the morning. However, the baby doesn't cry and Hayley sits cradling her as she lies there covered in blood, begging her child to breathe. Soon, Kat realizes there is a pool of water in the house and realizes that Hayley's waters must have broke. Keanu then comes rushing to find the Slaters and tell them that Hayley left him a message on her phone, saying she was in labour. Kat goes looking for her but soon finds that she took the taxi. After looking for a while, Kat hears the baby cry. They follow the cry and find Hayley and the baby, with Hayley lying there unconscious as her placenta has not yet came out. They phone the ambulance, who rushes them both to hospital as Keanu holds the baby in his arms.
When Hayley and the baby arrive at the hospital, Jean tells the doctor that Hayley has been high multiple times during her pregnancy and asks if that could affect the baby, but the doctor tells her it's too early to say. Once Hayley has woken up, she is horrified to find Kat holding the baby, with Mo said she is a proper Slater because she's so beautiful and immediately tells them both to leave and to put the baby down, as Hayley feels guilty that Kat is holding her Alfie’s baby, unknown to Alfie that Hayley had kept the baby instead of having an abortion, which he gave her the money for. Kat then starts to look through some old pictures of Alfie and the boys, telling Mo that they need their mother. The social worker then visits Hayley at the hospital, asking her how both she and the baby are doing, but Hayley screams at her to get out as they are doing fine. Hayley tells the doctors she doesn't want any more visitors just as Keanu walks in, which cheers Hayley up. He gives her a 'baby girl' balloon for the baby and kisses her head as he tells her well done. As he is about to go home, Hayley stops Keanu and asks him to stay with her. He does this, but during the night, Hayley sneaks out the hospital with the baby, thinking Kat will learn Alfie is the father and take revenge on Hayley, by making sure the baby gets taken away from her.