David Gautreaux David Gautreaux was a stage actor , slated to be featured as Lieutenant Xon in " " . However , the series was canceled , and it was decided to produce instead . Gautreaux was then recast in a minor role as Commander Branch of Epsilon IX station . The character of Xon was conceived after Spock performer Leonard Nimoy declined to reprise his role for the " Phase II " project . What was already known for quite some time in production circles , was made public on 22 October 1977 by Gene Roddenberry in a lengthy expose to hundreds of " Star Trek " fanclubs , finally confirming the rumors that had abounded for months . Negotiations with Nimoy had actually already been conducted since the 1975 " The God Thing " project , but by July 1977 it became clear that Nimoy had declined the rigors of a weekly television show . It was for this reason that the Xon and Commander Will Decker characters , dividing between them the characteristics of the role Spock played on , were conceived for the new series in the first place . ( " " , p . 39 ) By the time of the public announcement the search of the Xon performer was actually already completed . After his screen tests , Gautreaux was cast in the role on 26 September 1977 . However , his casting became somewhat unsettled for awhile as Majel Barrett , recast as Christine Chapel , raised some objections . Barrett , unaware that both the series concept ( " Phase II " was now a television movie ) and the character of Spock were already dropped and fearing that the " Original Series " " unrequited love of Chapel for Spock " plotline will not play well against an actor as young as Gautreux , requested an older actor against whom to play . A new screen test was called with both Gautreaux and an older British actor in mid - October , but the older actor ' s performance was " absolutely abominable " and Gautreux was definitively reaffirmed by the third week of October . ( " " , pp . 53 - 54 ) Purely by chance , Gautreaux became the very first performer who learned of the upgrade decision of " Phase II " to a full - blown theatrical feature film , nearly a month before the decision became formal , when he walked in on 21 October 1977 on an informal celebration , to sign his contract . At that moment , only three studio executives , four producers and a NASA consultant were privy to the decision made that day . " " It was a Friday evening : I ' ll never forget it . I don ' t think I ever saw the gates open when I came to the lot . I went to Gene Roddenberry ' s office ; there were men from NASA " [ note : Jesco von Puttkamer ] " ; there was a young Jeffrey Katzenberg ; there were people all toasting each other , celebrating , and I was so incredibly overwhelmed to be a part of it . But what they were celebrating was that they were going to make " Star Trek " into a major motion picture . And then we were going to do the series . And I thought , " Wow , this is incredible ! " " " , Geautreaux recalled . ( ; " Star Trek Movie Memories " , 1995 , pp . 77 - 78 ) The " we were going to do the series " remark was not actually true and only made for Geautreaux ' benefit as he was reassured that he was to play a major role in the movie , since he " was now a part of the family " . And indeed , at first this had no consequences for the Xon character , but after the movie ' s new Director Robert Wise had pushed for it , Spock definitively returned when Leonard Nimoy was signed on 27 March 1978 . ( " " , p . 101 ) As soon as he was confirmed , a frantic series of yet another round of rewrites was started to get the Spock character into the movie . This however , had now ramifications for Xon , as he was ultimately dropped as a principal character . Despite the reassurances for Gautreaux , nothing came of it and by summer ' s start , Xon was definitively struck as a principal character , replaced by the Commander Sonak character in a very minor – albeit a dramatic one as he was killed off in a transporter accident – role . Having emotionally invested in the role for months , but also because he did not want to be locked down as a stand - by performer as he had by then resumed his theater career , Gautreaux declined to appear as Xon in this capacity and instead accepted the somewhat larger consolation role of Commander Branch . Gautreaux shot his Epsilon IX scenes as second - unit photography in the summer of 1979 , long after principal photography had wrapped in January , and he has never interacted on - set with any of the principal cast . The studio , which had committed to a " play - or - pay " contract , compensated Gautreaux with $ 35 , 000 in September for him missing out on a signed lead role . ( " " , issue 139 , p . 13 ; " " , p . 77 ; " Star Trek Movie Memories " , 1995 , pp . 111 - 112 ) Gautreaux has never expressed any ill - will toward " Star Trek " for missing out on becoming a recurring part of one of the largest franchises in the industry , quite the contrary actually , as was evidenced when he received an unexpected invitation from Leonard Nimoy , who apparently harbored some residual remorse over the fate that befell Gautreaux , " Leonard and I had a meeting once when he called and asked me to down to Paramount . I thought it was because of " " . He had many roles to cast , and he wanted to meet with me . We had a nice long conversation , which is on videotape , because he recorded all of his conversations ; it helps him remember actors . We chit - chatted for a good period of time , and then he came in with what I call the slider , which was , " " How did you feel . . . how did it affect you . . . essentially , what did it do to your life when I came back and played Mr . Spock , thus removing your character ? " " I looked at him , wondering if he was trying to purge himself of something he had felt all this time . I asked him what he meant by that , and he said , " " Well , you were a young man and this was a very big moment in your life . Did I remove that moment ? " " I looked at him , with a thousand thoughts running through my mind . My response was , " " Look , I was young , but I wasn ' t brand new . I had been in this business , primarily in theater , for a good long time . For me Xon and " Star Trek " were like a play that opened and closed on opening night , which happens all the time in theater . I had , and continue to have , another life outside whatever Xon was or was not to be . " " He said , " " That ' s very good . I was hoping you would say something like that . " " I had no idea that he put that much investment and thought into the belief that he had upset my life . " Elaborating on the fact that his mental preparation for the Xon character had actually made him a better stage actor , Gautreaux has added , " " I have never felt badly , upset or any of those things for not playing Xon . I ' ve always felt that it was too bad the public didn ' t get a chance to see this character , given the preparation I had given to it . But insofar as how it enhanced my own life , they paid me back a hundredfold . Xon took me from a state of physical to a state of metaphysical , which is something that I ' ve never lost . " " ( " " , issue 139 , p . 14 ) In 1994 , Gautreux was interviewed in - depth by William Shatner for his memoir " Star Trek Movie Memories " about his involvement with the " Star Trek " franchise and these recollections , as transcribed , were the most elaborate ones Gautreux has ever given on his involvement to date . Subsequently , in 2001 , he was interviewed for a special feature on the DVD . In 2005 , he guest - starred in two episodes of Brannon Braga ' s short - lived series " Threshold " , which starred Brent Spiner . In 2008 , he guest - starred in an episode of " Boston Legal " , which starred William Shatner and John Larroquette .