Xon (David Gautreaux) never got to play this Vulcan character, now I wonder why? He was supposed to be the USS Enterprise NCC 1701 Science Officer in the never made Star Trek II, long story short Nimoy's I am not Spock soon switched when the idea of a multi million dollar movie was in the wind. The rest you can guess. Gautreaux got a small part in Star Trek the motionless picture.
Yangs are the bitter enemies of the Kohms in the less than subtle allegory that was "the Omega Glory."
Live Long and Prosper.