Robert Terwilliger one day accompanied his brother Cecil to an audition for the Krusty the Clown Show. While Cecil didn't get the part, it was "Bob" who got the part after impressing Krusty with an unannounced pie to the face. This act would go on to sew the seeds of jealousy and contempt in Cecil for his brother, and eventually come back to bite Bob later in life.
And so it went, for years Bob played second fiddle to Krusty as his sidekick. Like most people, Bob has a breaking point, and after being humiliated once too many times (Being shot out of a cannon in particular), he began to hatch a scheme of revenge to frame Krusty in an attempt to take over the show. While Homer was at the Kwik-E-Mart picking up ice cream and talking to Apu in an attempt to avoid going home to watch a slide show of his sister-in-laws Patty and Selma's vacation, Bob, in a Krusty the Clown disguise, held Apu up at gun point and robbed the place with Homer being a vital witness to the crime. This led to Homer fingering Krusty in a police line-up and later in court. With Krusty in disgrace and sent to prison, Bob was free to take over the show and add more educational qualities to its structure.
Bart Simpson, possibly Krusty's number one fan, was the only one to believe in his innocence. Together with his brainy sister Lisa, the duo set out to prove their hero's innocence. They managed to discover that the "Krusty" who robbed the store was reading a magazine, while the real Krusty can't read. Krusty also has a pacemaker, yet the "Krusty" who robbed the store was near a hotdog rotisserie, something people with pacemakers can't be near. The final piece of evidence came from video surveillance; when Homer backed up, he stepped on the tip of "Krusty's" shoe, thus causing him pain. However, the real Krusty has small feet which do not occupy the entire shoe. It didn't strike Bart who was behind it all until during a live taping of the show, Bob mentioned how he had "...Big shoes to fill.". Upon the realization, Bart revealed the truth, which in turn sent Bob to prison and brought Krusty his freedom.
Upon his release, Bob had continued a romance with Marge Simpson's sister Selma (They met through a prison pen pal system). Bob planned to marry her in order to cellect on a large some of money he'd inherit from a life insurance polity he had taken out on her. Much to Bart's dismay, they eventually did tie the knot. However, thanks again to Bart's keen eye, he was able to foil Bob's plot and save his aunt, thus sending Bob back to jail.
He was later yet again released on parole. However, this time Bart became his main focus and attempted to exact revenge upon Bart by murdering him. Bart and his family were relocated thanks to the witness protection program, yet Bob still managed to find them at their temporary boat house. Thanks to quick thinking and playing to Bob's ego, Bart managed to distract Bob with a musical number request long enough for the Springfield police to arrest him.
When he was next paroled, Bob decided to focus on politics, and ran for the position of mayor against then current mayor Joe Quimby and won in a landslide election. It was later revealed, thanks again to Bart and Lisa, that the election was rigged. Bob was then sent to jail for electoral fraud.
Bob later escaped from prison at an air show and stole a nuclear bomb. He demanded all television broadcasting be stopped, much to the chargin of Krusty the Clown (Krusty was so determiend to stay on the air and get all the TV ratings that he took over the emergency broadcast channel located in a shack). Bart and Lisa tracked Bob down and when the bomb was shown to be a dud, he kidnapped Bart and hijacked the Wright Brothers' plane in a kamikaze attempt on Krusty the Clown's life with hopes of also taking his own and Bart's life as well. Once again he failed and was sent back to prison.
Bob is later released into his brother Cecil's care with recommendation from Reverend Lovejoy. Cecil, who was still smarting over the blow to his ego that Bob was better than him at the Krusty the Clown Show audition, planned to blow up the Springfield Dam and frame Bob for it, while making off with the money that was to have gone into the Dam's production. However, Bob, along with Bart and Lisa, managed to foil his scheme and save the town (Temporarily, as the dam eventually broke anyway). Cecil still managed to have the last laugh as Bob was arrested along with him anyway thanks to Chief Wiggum's incompetence.
Bob, while back in prison, later learned that Krusty had taped over all of his old episodes with Bob as his sidekick. Feeling as though a part of his life had literally been ereased, Bob planned to kill Krusty at his anniversary ceremony, using Bart as a suicide bomber. However, Bob aborted his plan when Krusty revealed how sorry he was for the way he'd treated Bob. Bob and Krusty later seemingly make amends, yet Bob goes to prison anyway for attempting to kill Krusty.
Bob is then released by the Springfield Police Department to help find who has been making attempts on Homer's life (Later to be the son of Frank Grimes). Bob later tried to kill Bart, but found he couldn't after becoming so accustomed to his face. He then fled to Italy to make a new life for himself.
It was there he married, had a son, and became mayor of a small Tuscan village. The Simpsons met him on a chance encounter while there to pick up a car for Mr.Burns. They had a mutual understanding not to blow Bob's cover, but a drunk Lisa Simpson accidentally spilled the beans to the whole town, thus ruining Bob's new life, and causing him and his family to swear vendetta on the Simpsons.
Bob later fakes his death in a plot worked out with his family, including his brother Cecil, his mother and father, and wife and son. They managed to put Bart in the coffin, which was intended to be cremated. But this was halted thanks to Lisa and the other Simpsons and the Terwilliger family found themselves all in prison together.
Bob later switches faces with a fellow inmate, and when it was that inmate's turn to be released, it's Bob who gets paroled instead. As Walt Warren, Bob manages to move next door to the Simpsons. He tries to kill Bart on state lines which would have been legal, but ended up foiled and taken away by the state police.