 Nimoy, Leonard (qv) declined to return as Spock for the series, so  a new Vulcan character "Xon" was created to be the new science  officer. An employee of an agent was dating a young actor,  Gautreaux, David (qv), who had no agent of his own; she suggested  him for the part and he got it, then was told that it was actually  for a movie. When Nimoy finally agreed to do the movie, Spock  replaced Xon in the script and Gautreaux was given the smaller part  of Commander Branch.