Liam Sullivan, 74, actor on stage, screen and television series ranging from "Twilight Zone" to "L.A. Law." The Jacksonville, Ill., native started acting in small theater while a student at Illinois College and later at Harvard University. His dashing appearance took him from playboy to urbane roles in Broadway plays from "The Constant Wife" with Katherine Cornell to the recent Mike Nichols production of "The Little Foxes." Among the Los Angeles stage productions in which he appeared was the Ahmanson Theatre's "Mary Stuart." On the big screen, Sullivan had roles in the 1960s films "That Darn Cat" and "The Magic Sword." But he was best known for his prolific television career. He portrayed the villainous cattle baron Major Mapoy in the 1966-67 western series "The Monroes," guest-starred as a telepathic alien in "Star Trek," and had roles in soap operas and dozens of prime-time series including "Dragnet," "The Trials of Rosie O'Neill," "Dallas," "Falcon Crest," "Dynasty," "St. Elsewhere," "Magnum, P.I.," "Maude," "Bonanza" and "Little House on the Prairie." At the time of his death, Sullivan was working on two books: a novel and the history of his family's Eli Bridge Co., which was credited with inventing the Ferris wheel. On Sunday in Los Angeles of a heart attack.