...as Nagilum (1988).
Earl Boen (November 7, 1945-) played Nagilum in TNG: Where Silence Has Lease. He is best known for playing Dr. Peter Silberman in The Terminator, Terminator 2: Judgment Day and Terminator 3: Rise of the Machines. Besides Arnold Schwarzenegger, he is the only actor to appear in all three films.