Sideshow Bob
In a deliberate in-joke, he voiced Cecil, the brother of Kelsey Grammer-voiced Sideshow Bob, in "The Simpsons" episode "Brother from Another Series", in which the two characters parallel the Frasier–Niles relationship. At one point in the episode, Cecil mistakes Bart for Maris, the unseen wife of Niles on "Frasier". He returned as Cecil in the Season 19 episode "Funeral for a Fiend" where "Frasier" co-star John Mahoney voices Dr. Robert Terwilliger, Sr., the father of Cecil and Sideshow Bob.