Sideshow Bob used to be Krusty's sidekick and best friend and co-star of the Krusty the Clown Show, but in 1990 he was so tired of acting like an idiot that he framed Krusty for robbing the Kwik-E-Mart with a gun. Krusty was reported by Homer Simpson to the police and Krusty was thrown in jail. After Krusty's arrest, Bob gained control of the Krusty the Clown Show, renaming it Sideshow Bob's Cavalcade of Whimsy. Fortunately for Krusty, Bart foiled his scheme and he exposed Bob's crimes to the audience, and Krusty was released while Bob was thrown in prison, but not before swearing revenge on Bart for this.
Sideshow Bob is represented in the series, he is a sadistic psychopath obssesed by try killed (Bart), yet often very smart and sophisticated to talk.
Sideshow Bob enjoys the finer things in life, including reading classical literature and possesses massive. Likely due to his upbringing, he has a passion for theatre, knowing Gilbert and Sullivan's H.M.S. Pinafore off by heart as well as Shakespeare's works. In contrast to his love of the 'higher pleasures', he despises television and other 'low class' things, which gives him a rather snobbish attitude. Ironically, in his time when he was a Master Criminal, he studied the uses of Dynamite, which would theoretically be considered low class. At times, he also may have genuine desires to help humanity, as he explains that his motivation for tricking the Springfield citizens into electing him was to "save them from themselves."
Beneath the cultured gentlemen is the heart of a cold blooded killer; Bob is a man who thinks nothing of hurting others to get what he wants, even if this includes himself. Bob's primary motive seems to be revenge; his original crime (framing Krusty the Clown) was an attempt to get back at him for making a clumsy fool of Bob for years as his sidekick, and most of his other crimes have been more evil attempts at murdering Bart Simpson for foiling him. However, he has made several attempts at acquiring money and/or power, such as when he tried to kill Selma Bouvier or run a campaign for mayor as a republican (if for no other reason than to make the Simpsons miserable).