(written from a Production point of view)
Alfred Ryder (5 January 1916 – 16 April 1995; age 79), born Alfred Jacob Corn, was the actor who portrayed Robert Crater in the TOS episode "The Man Trap". He filmed his scenes between Monday 27 June 1966 and Thursday 30 June 1966 on Desilu Stage 9 and Stage 10.
Besides Star Trek, he made well over a hundred television guest appearances. These include stints on Outlaws (with future TOS co-star Leonard Nimoy), The Untouchables, Gunsmoke, The Outer Limits, Voyage to the Bottom of the Sea, The Man from U.N.C.L.E., Mission: Impossible, McCloud (with Diana Muldaur and Ken Lynch), Barnaby Jones (with Lee Meriwether), The Bold Ones: The New Doctors (directed by John Newland and featuring Whit Bissell and Ryder's "Man Trap" co-stars, Vince Howard and William Shatner), and Quincy, M.E. (with Robert Ito and Garry Walberg). He also had a role in the 1974 made-for-TV movie Indict and Convict, with his TOS co-star William Shatner and fellow TOS alumni Susan Howard and Michael Pataki. The following year, he was in the TV movie The Abduction of Saint Anne, with William Windom, James Gregory, Roy Jenson, and Vic Perrin.
Ryder co-starred with fellow TOS guest performers Kim Darby, Jeff Corey, Ron Soble, and John Fiedler in the classic 1969 Western True Grit. His other film credits include T-Men (1947), Hotel (1967, with Ken Lynch and Davis Roberts), The Stone Killer (1973), Escape to Witch Mountain (1975, with Lawrence Montaigne, Paul Sorenson, and Rex Holman), and the cult movie Tracks (1976, with Dean Stockwell).