Final answer:
David Hyde Pierce voiced the character Cecil Terwilliger on 'The Simpsons,' playing the brother to Kelsey Grammer's character Sideshow Bob.
Step-by-step explanation:
Actor David Hyde Pierce played the role of Niles Crane on the TV show 'Frasier' and also voiced the character Cecil Terwilliger on the show 'The Simpsons.' In 'The Simpsons,' Cecil Terwilliger is the brother of the infamous character Sideshow Bob, who is voiced by Kelsey Grammer. This special guest role by David Hyde Pierce created a unique situation where he once again played the sibling of a character portrayed by Kelsey Grammer, similar to their relationship on 'Frasier.'
The collaboration between Pierce and Grammer on both "Frasier" and "The Simpsons" showcases their versatility as actors and the chemistry that allowed them to successfully portray different sibling relationships in two distinct television series, adding depth to their contributions in the world of sitcoms. The shared experience created a unique connection for fans of both shows who appreciated the crossover between these iconic characters.