(written from a Production point of view)
Dallas Mitchell (8 October 1927 – 13 September 2009; age 81) was the actor who played Lieutenant Tom Nellis in the Star Trek: The Original Series first season episode "Charlie X". He filmed his scene on Friday 15 July 1966 at Desilu Stage 9. Mitchell has also made guest appearances on such television series as Gunsmoke, The Man from U.N.C.L.E., The F.B.I., Kojak, The Rockford Files, and Mission: Impossible.
Mitchell made his only feature film appearance co-starring with a number of other Star Trek alumni in the 1968 crime drama Madigan. The other TOS guest actors who had roles in this film are Michael Dunn, Steve Ihnat, Warren Stevens, Lloyd Haynes, Gloria Calomee, and William Bramley. Star Trek film actor Paul Sorenson and Star Trek: The Next Generation guest star John McLiam also appeared in the film.
Besides this, he appeared in several made-for-TV movies, including D.A.: Conspiracy to Kill (1971, with Steve Ihnat, Leslie Parrish, and Michael Strong), The Face of Fear (1971, starring Ricardo Montalban), Hijack (1973, with William Schallert), The F.B.I. Story (1974, with Gary Lockwood, Harris Yulin, Whit Bissell, Lenore Kasdorf, Bill Zuckert, and James B. Sikking), Conspiracy of Terror (1975, with Charles Cooper, Jon Lormer, Stewart Moss, and David Opatoshu), Amelia Earhart (1976, with Stephen Macht, Susan Oliver, Jane Wyatt, and Garry Walberg), and Tail Gunner Joe (1977, with Alan Oppenheimer, Andrew Prine, William Schallert, John Anderson, and Bill Quinn).
Mitchell died from cancer on 13 September 2009.