Krusty met Sophie's mother Erin while he was performing with a USO tour during the Gulf War. They had a romantic night of passion, but in the morning she realized she had to complete her mission—to assassinate Saddam Hussein. Krusty told Erin not to go, insisting that she had a new mission, to "get down with the clown". However, she left anyway and Krusty ended up tackling her just as she was about to kill Saddam with a rocket launcher, protesting that she couldn't kill Saddam because he was half of Krusty's act. Now angry with Krusty for ruining her mission, Erin began hating Krusty. She also came to hate clowns in general, and filled her house with artwork depicting violence against clowns.
Sophie first met Krusty during an autograph session, where she revealed to him that she was his daughter. Krusty said he wanted to reunite with Sophie's mother, but she rejected him.
Sophie loves to play the violin and she played for Krusty. He loved her performance, but later lost her violin in a poker game, and recruited Homer to help him get it back.
Sophie also likes to play soccer and was seen playing in a match where Homer was the referee.
Sophie spends Christmas with the Simpsons
Sophie and Krusty were attending the Pagan Winter Carnival together, when Krusty was trampled by the Strandbeest. In the hospital, Krusty was surprised to find out that Sophie was Christian, not Jewish and she wanted to celebrate Christmas. Marge offered to let them come over for Christmas at their house, and they both accepted.
When Krusty and Sophie turned up at the Simpson house, Sophie was unhappy because Krusty was using the invitation to film a Christmas special, A Very Krusty Christmas Special. Sophie got increasingly annoyed at what her father was doing as she wanted him to be spending time with her, not spending time with her and her friends for TV. Eventually, Sophie told Krusty to leave.
Krusty tried to make it up to Sophie by becoming a Christian. He started attending church and became closer to Sophie, who was happy that he was trying to make her happy. Krusty even changed his show to make it more Christian and had Sophie as a guest on it, playing the french horn. Eventually, Krusty went to get baptized in the icy river but fell in and almost drowned. When he came out, he decided not to become Christian. Sophie, however, was happy that he put the effort into making her happy and reconciled with him.
Later, Krusty and Sophie were taking a sleigh pulled by the Strandbeest to a winter feast, whilst singing "Sleigh Ride".