William Sargent William Sargent is the American actor who played Dr . Leighton in , a first season episode of . In addition to this role , Sargent has credits in two films and about thirty television shows . Born in Berlin , Germany , he currently resides in Salt Lake City , Utah . He filmed his scenes for the episode on Tuesday at Desilu Stage 10 and on Thursday , at Desilu Stage 9 . Career . Besides " Star Trek " , Sargent guest - starred on two other Desilu - produced series , " The Untouchables " and " Mission : Impossible " . On the former , he appeared in an episode directed by Robert Butler , who previously directed Sargent on an episode of " Stoney Burke " with Lee Delano and Kenneth Tobey . On " Mission : Impossible " , Sargent appeared in an episode with John McLiam . Sargent also appeared in two episodes of Rod Serling ' s classic science fiction series " The Twilight Zone " in 1963 . That same year , he was seen in two episodes of " Alfred Hitchcock Presents " , and appeared in a third episode with David Opatoshu the following year . In 1967 , Sargent guest - starred in two episodes of the science fiction series " The Invaders " : one with Bill Erwin , Jonathan Lippe , Dallas Mitchell , and Phillip Pine , and another with Whit Bissell and Andrew Prine . In addition , Sargent had a two - episode recurring role on the situation comedy series " My Three Sons " in 1963 , having appeared as a different character on the show the previous year . He then appeared in several episodes of " The F . B . I . " , including two in 1966 with Stephen Brooks ( who was a regular at the time ) and one in 1970 with Antoinette Bower . Sargent later had a brief recurring role on " Cannon " , during which time he worked with Barbara Babcock , the aforementioned Bill Erwin , Fritz Weaver , and Anthony Zerbe . A 1966 episode of " 12 O ' Clock High " entitled " The Survivor " had Sargent working alongside Seymour Cassel and fellow TOS guest performer Jill Ireland . Sargent later appeared in two 1974 episodes of " Barnaby Jones " , on which Lee Meriwether was a regular ; Teri Garr and Mariette Hartley also appeared in one of those episodes . Sargent ' s other TV credits include episodes of such programs as " Combat ! " , " Voyage to the Bottom of the Sea " , " Dr . Kildare " , " The Fugitive " , " Mannix " ( in an episode with Stanley Adams , Barry Gordon , and James Greene ) , and " The Streets of San Francisco " ( working with Byron Morrow ) . Sargent had an uncredited role in ' s 1961 drama film " The Young Savages " , as did Stanley Adams , Clegg Hoyt , and Bill Quinn . In 1969 , Joseph Sargent ( no relation ) directed William Sargent in the unsold television pilot movie entitled " The Immortal " . In addition , Sargent can be seen in the 1972 made - for - TV movie " A Great American Tragedy " with William Windom . He also had a supporting role in the 1974 independently - produced blaxploitation film " The Take " , along with John Chandler . Following a 1975 episode of " S . W . A . T . " with George Murdock , Sargent ceased acting in either film or television . He made a brief return to the screen in the 1990s , appearing in the 1997 made - for - TV movie " Not in This Town " . Ed Begley , Jr . was among the lead actors in this film .