(written from a Production point of view)
Marc Daniels (born Daniel Marcus) (27 January 1912 – 23 April 1989; age 77) was a director of many Star Trek: The Original Series episodes. With a complete 14 episodes on his credit (if counting "The Menagerie, Part I" and "The Menagerie, Part II" as a single episode), he is tied with Joseph Pevney in directing the most number of Original Series episodes. He also wrote an episode of Star Trek: The Animated Series, although he had only one other writing credit in his long television career. Daniels also wrote an undeveloped story outline, entitled "The Beast" for Star Trek: The Original Series. 
Earlier in his career, Daniels directed the first 38 episodes of I Love Lucy, which started his long association with Lucille Ball and Desilu. In 1961 he directed an episode ("In the Highest Tradition") of Gene Roddenberry's The Lieutenant, starring Gary Lockwood. The episode guest starred Leonard Nimoy and Majel Barrett. In 1974 he directed Roddenberry's failed pilot entitled Planet Earth, which featured Ted Cassidy, Diana Muldaur, Majel Barrett, Craig Hundley and Patricia Smith. Robert H. Justman served as producer in that project.
Besides this, during his 41-year career as a television director, Daniels helmed episodes of such series as The Man from U.N.C.L.E., Gunsmoke, Ben Casey, Mission: Impossible, Bonanza, Hogan's Heroes, Kung Fu and Barnaby Jones (starring Lee Meriwether.)
According to Robert Justman, Daniels "was a marvelous talent and a wonderful man. And what a find for Star Trek!" And "his film work was outstanding, crisp and energetic". (Inside Star Trek: The Real Story, pp. 203-204)
From 1951 to his death, Daniels was married to Emily Hosmer, who worked as a camera coordinator for I Love Lucy. Together, they had three adopted children, Amy, Polly and David. Mrs. Daniels died in 2011.