Robert Terwilliger, Sr. is Sideshow Bob's father. In reality, Bob was injected with a death simulation drug by his father prior to the fated trial in order to conduct a complex plan to kill Bart Simpson via locking him in a coffin and cremating him. He, and the rest of the Terwilliger family, are in prison.
He guest starred on The Simpsons as Sideshow Bob's younger brother Cecil. He first appeared in Season 8's "Brother from Another Series", and ten years later in "Funeral for a Fiend". He appears again as himself in the Season 26 premiere. He is best known for playing Frasier Crane's brother Niles on the sitcom Frasier.