(written from a Production point of view)
Lou Antonio (born 23 January 1934; age 84) played Lokai in the Star Trek: The Original Series episode "Let That Be Your Last Battlefield". He filmed his scenes between Monday 7 October 1968 and Monday 14 October 1968 at Desilu Stage 9.
Though they did not share any scenes, Antonio had earlier appeared with William Shatner in a 1962 episode of The Naked City called "Portrait of a Painter". He also did an episode of For The People, the show Shatner starred in just before Star Trek. The two of them also worked together in a 1970 TV movie called Sole Survivor, which also featured TOS regular John Winston. He also appeared in a 1963 episode of The Naked City entitled "Color Schemes Like Never Before", which was directed by Ralph Senensky.
Antonio once appeared in an episode of Here Come the Brides, a show which featured Original Series veterans Robert Brown, Mark Lenard and David Soul. The episode also featured Trek veterans Arlene Martel and James B. Sikking.
Antonio left acting by the late 1970s to become a television director. He has directed Shatner in episodes of Boston Legal, a show which also starred Star Trek: Deep Space Nine actor Rene Auberjonois. In one of the Antonio-helmed episodes, the ringtone used by Shatner's character, Denny Crane, is a TOS-era communicator chirp. Joanna Cassidy, who played T'Pol's mother T'Les on Star Trek: Enterprise, appeared in that episode. Another of the episodes he directed featured Armin Shimerman, Ethan Phillips and Ron Canada.