(written from a Production point of view)
Melvin Mouron Belli (29 July 1907 – 9 July 1996; age 88) is most famous as a criminal defense and personal injury lawyer, not an actor, but additionally played the role of "Gorgan" in TOS: "And the Children Shall Lead". He filmed his scenes for the episode on Monday 1 July 1968 and Friday 5 July 1968 at Desilu Stage 9.
Among his many legal accomplishments are the defense of Jack Ruby, the man who murdered Lee Harvey Oswald, and numerous refinements to personal injury litigation, including "day in the life" films designed to graphically demonstrate the impact of injuries on their victims. He was also the defense attorney of Mick Jagger and The Rolling Stones.
In 1954, his accomplishments led Life magazine to dub him the "King of Torts." Walter Koenig objected to his playing the role of "Gorgan", believing the role should have gone to someone in the acting business. (Captains' Logs: The Unauthorized Complete Trek Voyages) Fred Freiberger said of Belli, "He wasn't the greatest actor in the world, but was very cooperative [....] He was fun to work with." (The Star Trek Interview Book, p. 164) He was the father of Caesar Belli, who played Steve O'Connel in the same episode.
He had a peripheral role in the investigation of the "Zodiac" killings, which took place in the San Francisco area between 1969 and 1973, and was portrayed by Brian Cox in David Fincher's 2007 film Zodiac, which dramatized those events. The film includes a reference to Belli's guest role in Star Trek.
He died in 1996 of complications due to pancreatic cancer.