(written from a Production point of view)
Steve Diamond is an actor who was a regular background performer on Star Trek: Deep Space Nine and also appeared in Star Trek Generations. His costume from Generations was sold off on the It's A Wrap! sale and auction on eBay. 
Rick Berman, along with Ronald D. Moore and Brannon Braga were upset with Diamond during the scene in Generations in which he can be seen pumping his fist and saying "Yes" shortly before Brent Spiner as Data in front of him does the same. They felt Diamond had stolen the moment from Spiner and were unable to reshoot the scene. (Star Trek Generations Special Edition DVD audio commentary)
Diamond appeared in episodes of Bosom Buddies (1982, with George Murdock) and Time of Your Life (1988).
Star Trek appearances
(This list is currently incomplete.)