5. Robert Terwilliger Sr
Dr. Robert Terwilliger Sr appears in the 2007 episode 'Funeral for a Fiend' and is the father of 'Sideshow' Bob and Cecil Terwilliger. When Sideshow Bob is put on trial for yet again trying to murder the Simpson family, Robert goes on record to say his son suffers from an illness caused by his desire to kill Bart. Robert is later found to be part of a larger plot when Bart throws Bob's medication out of a window believing them to be biological weapons, causing Bob to 'die' - Robert had actually injected his son with a 'death simulation drug' to give Bob the appearance of a corpse at his 'funeral', as part of a complex plan to kill Bart by locking him in a coffin and cremating him. He, along with the rest of the Terwilliger's, is in prison.