Fat Tony is the quinary antagonist of The Simpsons. He is the resident mafia crime lord. Although a comical take on the typical Italian-American stereotype he can be a geniune threat to other residents of Springfield and has varied from being used for comedy to being a fairly serious character, depending on the story.
Fat Tony's life seems to revolve around crime, in a similiar fashion to Snake, however unlike the anarchic Snake - who commits crime at random and is often imprisoned Fat Tony is a more subtle but no less dangerous criminal who commits his crimes (largely) in secret.
Fat Tony and his minions have had a few run-ins with Homer Simpson and his family, sometimes coming very close to killing the icon but always having their schemes foiled in some way or other.
In the season 22 episode "Donnie Fatso", Fat Tony dies of a heart attack. However, he is somewhat "revived" when his cousin Fit Tony takes over his job, gains weight, and is soon given Fat Tony's name.