Martin Mull was born in Chicago in 1943, but was raised in Ohio. He studied painting at the Rhode Island School of Design. In 1976, Mull got his break into acting as portraying a set of twins in the absurdist soap opera Mary Hartman, Mary Hartman.
Since then, Martin has appeared in over 120 films and TV shows. He is best known for his role of Leon Carp in 46 episodes of Roseanne and as Principal Willard Kraft in 73 episodes of Sabrina the Teenage Witch.