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 had only one thing on his mind: Bart's death. For his next evil plan, he was released from jail and married Bart's aunt Selma. Later, he tried to blow her up to gain her inheritance from the stock market, but Bart caught on to his plan and Selma was rescued and Bob was arrested again. Later, Sideshow Bob began sending death threats to Bart in the mail. Bob was later released and drove around an ice cream truck reading a list of the people he would spare (Bart was not on the list). In response, Bart and his family moved from Springfield to another town and changed their surname to Thompson. However, Bob latched himself onto the Simpson's car and resumed his pursuit after Bart, but was hit by rakes, which allowed Bart to flee and alert his parents. Later that night, Bob located the family in a boat used as a home and upon boarding, he cut the rope holding the boat to the dock and tied up Bart's parents and sister Lisa. Bob eventually cornered Bart on the port, but Bart stalled for time by distracting Bob long enough for the boat to reach Springfield. Bart's plan to defeat Bob again was successful, and the police freed Lisa and Bart's parents after the boat arrived in Springfield and yet again arrested Bob.
Later, Bob was released again and ran against Mayor Quimby for mayor of Springfield. Bart and Lisa ran for Quimby, but despite that, Bob rigged the election against Mayor Quimby by putting in dead people and pets as people who voted for him and won the election. After becoming mayor, Bob put the Simpson's house in front of his expressway to demolish it and demoted Bart to kindergarten. Bart and Lisa desperately tried to find evidence that Bob rigged the election, to no avail. However, Bart discovered one of the names of the people who voted for Bob on a tombstone with help from Waylon Smithers. Bart and Lisa placed charges against Bob and put him on trial, where they tricked him into confessing his crime and Bob was arrested. His evil plans had failed again. Later, Bob was placed on duty in a local Air Force Base, but escaped and stole an A-bomb to threaten Springfield to rid itself of television, and the Air Base was evacuated, but Bart and Lisa were separated from their parents and decided to stop Bob. The National Guard soldiers searched for Bob, but were unable to locate him. Bob was broadcasting from an airship and was able to evade capture easily. However, Bob discovered that Krusty began televising himself from a fallout shelter in the desert. This outraged Bob, but not before Bart and Lisa tracked him in the cockpit. Angry, Bob attempted to detonate the A-bomb, but it turned out to be a dud and did not explode. Lisa quickly used the airship's electronic ticker to send a message to the police. When the police tried to capture Bob, Bob kidnapped Bart and deflated the airship. Bob then stole the Wright Brother's plane to escape and crash into Krusty's shelter. However, Bart freed himself and Bob crashed the plane near the shelter where the police arrested him.
Later, Bob was released into the care of his younger brother, Cecil, who began constructing a dam, but Bart and Lisa snuck in to investigate, but Bob caught them and returned them to their parents. Later, Cecil revealed his plan to flood Springfield, but was foiled by Bart and Lisa. Bob was arrested shortly after. Later, Bob escaped prison and tracked down Bart to Springfield Elementary School and lured him into a shed where he hypnotized him. Bob planned to use Bart to kill Krusty. Eventually, Bob strapped explosives to Bart to kill Krusty and kill Bart himself so Bob could finally have his revenge. However, Krusty's monkey detached the explosives and destroyed Bob's chamber, which also forced Bart out of his hypnotic state. Bob survived, but was finally arrested.
Some time later, Bob was released to help find out who attempted to kill Homer Simpson, despite Bart's concerns. The police attached an electric collar to Bob's neck to prevent him from killing Bart. Eventually, Bob discovered the assassin was Frank Grimes, Jr., the son of Frank Grimes, who had a hatred against Homer as well electrocuting himself to death while mimicking Homer's habits. Bob and Homer eventually caught Frank and he was arrested. After Frank's imprisonment, Bob returned to his goal of killing Bart, and attempted to murder him after his parents left the room, but didn't because he "grew accustomed to his face." He let Bart go and went out his window ready to escape in the shadows, but the bird activated the shock remote that Bob threw out earlier, which electrocuted Bob. However, Bob fled to Italy and married a Italian woman named Francesca Terwilliger, who would later give birth to his son, Gino Terwilliger. Eventually, Bob became mayor of a village. The Simpsons soon arrived to buy a new car for Homer's boss, Mr. Burns, and confronted Bob, who warned them not to expose him. However, Lisa became intoxicated and exposed Bob's criminal past in the village, which infuriated Bob, and he swore vendetta on the Simpsons. Bob pursued the Simpsons on a Ducati, but failed to catch them. Later, Bob cornered the Simpsons in the Colisseum with his family, but the Simpsons were rescued by Krusty and they returned to the U.S., leaving Bob stranded in Italy.
Eventually, Bob snuck into the U.S. and trapped the Simpsons in a restaurant. However, the police caught on and Bob was arrested. However, Bart was put on trial as well by Bob, and Bob ignited what appeared to be an explosive, but Bart threw his heart medication out the window, and Bob supposedly died. However, Lisa discovered that Bob's family planned the whole thing out and Bob trapped Bart in a coffin and attempted to cremate him, but was foiled by Lisa when the police rescued Bart and arrested Bob. Later, Bob's cell mate, Walt Warren, was scheduled for early release. and drugged him unconscious. Bob used plastic surgery to switch his face with Warren's face. Using Warren's identity, Bob escaped prison while Warren stayed in prison, as the police mistook him for Bob. Bob then bought the house next to the Simpson's house, but Bart immediately discovered who he really was. Bart made several attempts to blow Bob's cover, but with little success. Later, his mother Marge took Bart to see Bob, who was really Warren, still in jail, which appeared to satisfy his concerns. That night, Warren escaped from jail to alert the Simpsons of the danger. Later, Bob bought an extra ticket to the baseball game. Bart agreed to go and went to get his cap. Bart then left with Bob, where he revealed he was indeed Bob and proceeded to take Bart to Five Corners to kill Bart. Once he arrived at Five Corners, Bob revealed his plan: Bob would stand in one state, fire his gun in the second state, where the bullet would travel through the third state, hitting Bart in the fourth state, and Bart falls dead in the fifth state, so his murder cannot be prosecuted. However, Warren, attacks Bob and stopped him. The police then arrived to capture Bob, and Chief Wiggum revealed that Bart was never truly convinced that Bob was Warren, and before his capture, Bart reported to the police about Bob and told them to track the car. However, Bob jumped to another state, but the police appeared there as well. Eventually, Bart was freed and Bob was arrested and Warren with them to return their faces to normal, and Bob was seemingly placed in high security shortly after.
As Sideshow Bob is represented in the series, he is a sadistic psychopath obsessed by try kill a child (Bart), yet often very smart and sophisticated to talk.
Sideshow Bob enjoys the finer things in life, including reading classical literature. 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 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).