here is an excerpt from an episode guide that started it all for Fat Tony
39. Bart the Murderer
Bart awakes in a good mood because he is going on a field trip to a chocolate factory. His day quickly takes a turn for the worst though and it really gets bad when he forgets his permission slip. He has to stay at school licking stamps for Principal Skinner. He rides his skateboard home and stumbles into an Italian gangster's operation. The leader, Fat Tony immediately takes a shine to him. He hires Bart to be his errand boy and Bart soon figures out that they are crooks. Bart becomes a gangster, and when Skinner gives him problems, Fat Tony goes to have a little talk with Skinner. Later that same day, Skinner vanishes and Bart thinks that Tony has killed him. Bart goes on trial as an adult for ordering them to kill Skinner. They act as though he were their capo. Just before Bart's sentence, Skinner waltzes into the courtroom. He tells about how an old stack of newspapers had trapped him in his home. Bart goes free and parts ways with Fat Tony, and then he watches the FOX made-for-TV movie about his life.
Joe Mantegna is the voice of Fat Tony and his crew has been a recurring character in the Simpsons ever since.