Cassidy's height gave him an advantage in auditioning for unusual character roles. His best-known role is Lurch on "The Addams Family", in which he feigned playing the harpsichord(although he was an accomplished organist. He also played the character named Thing, while associate producer Jack Voglin would take over the role in scenes with both characters. Though the character of Lurch was originally intended to be mute, when Cassidy ad-libbed "You rang?" in response to the butler call, the subtle humor and the deepness of his voice was immediately a hit. "You rang" became his signature line, and more speaking parts were written for him. Several episodes were written to feature Lurch.