Dr. Robert Terwilliger, Sr., also known as Dr. Robert, is Robert and Cecil Terwilliger's father.

When Sideshow Bob was put on trial for trying to kill The Simpsons, he claimed that Bob had suffered from an illness caused by his desire to kill Bart Simpson. Bart threw Sideshow Bob's medication out of a window (believing it to be a biological weapon). This subsequently caused Sideshow Bob to "die". 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, were sent to prison afterwards for 87 years.

Behind the Laughter

Robert Terwilliger Sr. was voiced by the late John Mahoney, who also plays the father of the two brothers in Frasier. The two brothers are voiced by Kelsey Grammer and David Hyde Pierce the voice actors of Sideshow Bob and Cecil Terwilliger, who are brothers in The Simpsons. Kelsey and David also star as Frasier and Niles Crane respectively.


  • He has many similarities with the Mayo Clinic Doctor, such as his face and hair.
  • Though Sideshow Bob gets his hairstyle from his mother, he and his father appear to have a similar facial structure.


Terwilliger Family
Robert Terwilliger Sr. | Dame Judith Underdunk | Sideshow Bob | Cecil Terwilliger | Francesca Terwilliger | Gino Terwilliger
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