 The inventive comedian known for his roles in Roseanne and Clue has died. Martin Mull was 80 years old. From member station WKSU, Kabir Bhatia reports. Mull worked in visual art, music, and stand-up before moving into acting in the late 1970s. Some of his notable roles include Colonel Mustard in Clue, Leon Karp on Roseanne, and Ron Richardson in 1983's Mr. Mom, where he shared a memorable scene with Michael Keaton.