Sideshow Bob

From Simpsons Wiki

Robert Underdunk Terwilliger, aka Sideshow Bob,first appeared briefly in the episode "The Telltale Head". His first major appearance was in "Krusty Gets Busted".

Sideshow Bob was originally the sidekick on Krusty the Clown's television show, but Krusty's continuous abuse led to Bob framing him for armed robbery. Krusty was arrested and Bart Simpson discovered that Bob was behind the crime, leading to Bob's arrest. Since then he has been Bart's mortal enemy, and has tried to kill Bart (but has been unsuccessful in every attempt) in

Trivia

Sideshow Bob is voiced by Kelsey Grammer,