 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. I'm going to rip these walls out and, of course, rewire it. Yeah, are you going to make it all 220? Yeah, 220, 221, whatever it takes.