(written from a Production point of view)
Marc Grady Adams (born 9 October 1925; age 94), sometimes credited more simply as Marc Adams, is the actor who played Prince Hamlet in the Star Trek: The Original Series first season episode "The Conscience of the King".
He also appeared in a 1967 episode of Mission: Impossible which, like TOS, was produced by Desilu Studios before Paramount Pictures merged with it and by Paramount Television afterwards. In 1984 he was in episodes of Hardcastle & McCormick (starring Brian Keith and Daniel Hugh Kelly) and Webster.
He had a role in the 1992 TV-movie Sinatra (with Brad Blaisdell, Christopher Carroll, Jeff Corey, Robin Gammell, Bruce Gray, Bob Gunton, David A. Kimball, Jay Robinson, Jack Shearer, Don Stark, and Todd Waring). He later appeared in a 1996 episode of Arli$$ and the 2005 feature film Interviewing Norman.