Why does Sideshow Bob want to kill Bart Simpson?

The character of Sideshow Bob began his career as the non-speaking sidekick on Krusty the Clown's television show. The episode "Brother from Another Series" (season eight, 1997) reveals that Bob only received the job after his younger brother, Cecil failed an audition, because Krusty considered Bob to be a perfect comic foil. After repeated instances of abuse, including being shot from a cannon and hit constantly with pies, the Yale-educated Bob became angry at Krusty and resentful of the clown's success. In "Krusty Gets Busted" (season one, 1990) Bob disguised himself as Krusty and framed him for armed robbery of the Kwik-E-Mart. After Krusty is arrested, Bob takes control of the show, introducing children to elements of high culture. However, Bob's reign is short-lived; Bart Simpson exposes the plan, Krusty is released, and Bob is sent to jail.

In "Black Widower" (season three, 1992), Bob's first major appearance after framing Krusty, he is released from prison and marries Bart's aunt, Selma Bouvier. As part of a scheme to inherit money she has invested in the stock market, Bob attempts to blow Selma up during their honeymoon. Bart again foils the plan and Sideshow Bob returns to prison.