|Portrayed by||Jessie Wallace|
|First Appearance||18th September 2000 (2000-05, 2010-PRESENT)|
|Address||23 Albert Square|
|Occupation||Market stall holder|
|Husband||Alfie Moon (2003–13, 2014-)|
|Romances|| Derek Branning (2012) |
|Sons|| Tommy Moon |
|Sisters|| Lynne Slater |
|Grandmothers|| Mary Slater |
|Uncles|| Harry Slater |
|First cousins|| Zoe Slater |
|Other relatives|| Sean Slater |
Kathleen "Kat" Moon is played by Jessie Wallace. She constantly lies about her age, whereas she is 43, born in 1971. She first arrived in Albert Square in 2000 and left for a short time in 2004. She returned to the show for a couple of months in 2005 before leaving again on Christmas Day. In 2010, she returned with husband Alfie, heavily pregnant after she had sex with Michael. She gave birth at the end of 2010 to a baby boy named Tommy. Local resident Ronnie swapped her stillborn son James with Tommy on New Year's Eve and for months Kat believed her son was dead. Four months later it was revealed that Tommy was alive and well and was being raised by Ronnie as James. Kat briefly left Walford in 2011, but returned in June 2012 when she was told by Alfie, who had had a phone call from Mo, that Jean was unwell. It was revealed in December 2012 that Kat had been cheating on Alfie with Derek Branning and Alfie forcefully threw her out of The Queen Vic. On Christmas Day 2012, Derek died of a heart attack, and throughout 2013, Kat's storylines have evolved around her trying to win Alfie back from his new girlfriend, Roxy Mitchell. Kat and Roxy shared a feud and have had two catfights, one in October 2010 and another in February 2013. Kat revealed to Alfie that she was pregnant on Christmas day in 2013. Shortly after Kat has a fall, and at the hospital her and Alfie discover that she is having twins.
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 with 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 in fact Michael Moon's baby - Alfie's 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.
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 affair 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 the 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 drop the charges if she changed her alibi the 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 on 8th August whilst visiting Jean in Hospital.