(written from a Production point of view)
Donald James Marshall (born 2 May 1936; age 79), better known simply as Don Marshall, is the actor who played Lt. Boma in "The Galileo Seven", a first season episode of Star Trek: The Original Series. He is perhaps best known for his role as Dan Erickson on the television series Land of the Giants.
Marshall was born in San Diego, California and is one of four children. Although initially studying to be an engineer in the late 1950s, he was encouraged to become an actor by a friend while serving in the United States Army. Marshall studied acting at the Bob Gist Dramatic Workshop while simultaneously studying Theater Arts at Los Angeles City College.
In addition to acting, Marshall has provided consultation regarding his work and racial issues, and as a result was once given an award for "Outstanding Achievement in his field as a Black Achiever in the United States".  Marshall was once married, but he and his spouse, Diane, have since divorced. 
Marshall made his film debut with an uncredited role as an intern in the 1962 drama The Interns. This film also featured an uncredited appearance by Peter Brocco, who, like Marshall, later appeared on Star Trek: The Original Series. Later TOS director Jud Taylor made an uncredited appearance in the movie, as well. Marshall's next feature film was the 1964 drama Shock Treatment, in which he and Ed McCready both made uncredited appearances.
After Land of the Giants came to an end, Marshall landed a supporting role in the cult, B-grade 1972 science fiction-horror film The Thing with Two Heads, in which a racist white man has his head transplanted onto the body a black death row inmate. Among the actors Marshall worked with on this movie was Roger Perry, a fellow TOS guest star. Marshall then starred in the 1973 science fiction thriller Terminal Island, which also featured Sean Kenney, and played a henchman in the 1974 Sidney Poitier-directed comedy Uptown Saturday Night.
Marshall's latest film credit is a Hungarian animated film from 1975 called Hugo the Hippo. Marshall lent his voice to the English-language version of this film, as did fellow TOS guest actor Percy Rodriguez.
1963 – 1968
Marshall's first television work was the NBC anthology series Kraft Suspense Theatre in a two-part 1963 segment entitled The Case Against Paul Ryker. The two segments were later edited together and released as a film, Sergeant Ryker, in 1968.
In 1963, Marshall starred opposite TOS actress Nichelle Nichols in the CBS movie Great Gettin' Up Mornin', which aired in January 1964. In this movie, Marshall and Nichols portrayed African-American parents preparing their children for their first day at a racially integrated school in America's south. Shortly after shooting this movie, Marshall and Nichols again worked together in an episode of Gene Roddenberry's pre-Star Trek series, The Lieutenant, which starred fellow TOS alum Gary Lockwood. The episode, "To Set It Right", was directed by Vincent McEveety.
Marshall and fellow TOS veteran William Marshall both guest-starred in a 1964 episode of Rawhide. Marshall reprised his role in another episode later that same year. In 1965, Marshall was cast in an episode of the medical drama Ben Casey by John Meredyth Lucas, who later wrote, produced, and directed for TOS. Marshall then had a recurring role as Luke in the CBS series Daktari, appearing in three episodes.
His subsequent television credits include guest spots on such series as Mission: Impossible (with William Smithers and Michael Barrier), 12 O'Clock High (with Lloyd Haynes), Dragnet 1967 (with Hal Baylor and Dick Miller), Tarzan (with George Murdock and again working with William Smithers), and Ironside (which starred Barbara Anderson]]). Marshall also played the recurring role of Ted Neumann on the NBC sitcom Julia. He was one of three Star Trek alumni to play Julia Baker's love interest on this show; the others were Paul Winfield and Fred Williamson.
Land Of The Giants and beyond
Marshall is perhaps best known for playing Dan Erickson on the Irwin Allen-produced television series, Land of the Giants, from 1968 through 1970. He credited his previous experience in football, track, and pole vaulting with helping him perform the required stunts for the show.  Since the series ended, Marshall has written a script for a potential revival called Escape from a Giant Land. 
When his work on Land of the Giants was finished, Marshall landed a guest spot on the classic sitcom Betwitched, where he acted with Parley Baer. He then had a role in the TV movie The Reluctant Heroes aka The Egghead on Hill 656, in which he played an Army private who was subjected to on going racial abuse by a colonel. Later, Marshall guest-starred in two episodes of Police Woman, including one co-starring James Gregory and Susan Oliver and another directed by Alexander Singer.
Herb Kenwith, the director of the TOS episode "The Lights of Zetar", directed Marshall in a 1976 episode of the sitcom Good Times. Marshall subsequently worked with "Errand of Mercy" director John Newland on the TV movie The Suicide's Wife in 1979. Majel Barrett also had a role in this movie.
Marshall appeared in the 1977 TV movie Benny and Barney: Las Vegas Undercover along with Ted Cassidy, after which he was seen in the 1978 TV special Rescue from Gilligan's Island. Vincent Schiavelli can be seen in this production, as well. In 1979, Marshall guest-starred on the cult sci-fi series Buck Rogers in the 25th Century, playing Julio in a two-part episode. Tim O'Connor was a regular on this series at the time.
Between 1978 and 1980, Marshall made three appearances on The Incredible Hulk, each time as a different character. He then appeared in an episode of Little House On The Prarie, playing a doctor confronted with racism who ultimately proves himself by performing an emergency C-section. In 1984, Marshall was cast in the role of Senator Ed Lawrence on the relatively short-lived soap opera Capitol. However, his character was recast the following year; the actor chosen to replace him was Michael Dorn, later of Star Trek: The Next Generation fame.
In 1992, Marshall made an appearance in the TV movie Highway Heartbreaker, as was Brock Peters. This is Marshall's last on-screen appearance to date.