William co-starred with his cousin Paul Winfield in Twilight's Last Gleaming (1977).
William died exactly 4 years later, on the same day, as his Star Trek co-star DeForest Kelly, from when he guest-starred on the episode "The Ultimate Computer" as Dr. Richard Daystrom.
William appeared in television commercials for Pee-Wee's Playhouse when it was released on home video in 1996.
William took his role as "The King Of Cartoons" in Pee-Wee's Playhouse on the request of his grandchildren.
William was 6 feet 5 inches tall.
Marshall is the cousin of the late Paul Winfield.