(written from a Production point of view)
Eugene "Gene" Lee Coon (7 January 1924 – 8 July 1973; age 49), commonly known as "Gene L. Coon", sometimes credited under the pseudonym "Lee Cronin", was a writer and producer for Star Trek: The Original Series. He produced the first season of the series from "Miri" to "Operation -- Annihilate!" and the second season from "Catspaw" to "A Private Little War", earning him a 1967 Emmy Award nomination.
Coon was hired as line producer in August 1966, when associate producer / story editor John D.F. Black left, and Gene Roddenberry felt he needed someone to handle everyday production business and do re-writes of the scripts, or else he and Robert Justman would soon be unable to cope up with the demanding work. He was Roddenberry's fourth choice for the job, as Fred Freiberger, Samuel A. Peeples, and James Goldstone all declined the offer. (These Are the Voyages: TOS Season One, 1st ed, p. 245)
Upon being hired by Roddenberry, an enthusiastic Coon had nothing but praise for the strictly to scientific believability adhering creator of the series,
"Gene created a totally new universe. He invented a starship, which works, by the way, and is a logical progression from what we know today. He created customs, morals, modes of speaking, a complete technology. We have a very rigid technology on the show. We know how fast we can go. We know what we use for fuel. We know what our weapons will do. And Gene invented all these things. He did a monumental job of creation. He created an entire galaxy, and an entire rule book for operating within that galaxy, with very specific laws governing behavior, manners, customs, as well as science and technology. Now, that's a hell of a job. He didn't create a show. He created a universe, and it works, and it works well. This was a massive, titanic job of creation. One of the most impressive feats of its kind that I've ever seen. You can submit our ship or our technology or anything you want to NASA and they will say, "Well, it's pretty far out, but I don't see why it shouldn't work." Nobody can tell us that it's scientifically impossible or that it won't work." (The Making of Star Trek, p. 74)
The lavish praise for Roddenberry notwithstanding, Coon himself contributed substantially to the "totally new universe", as much of the framework of the Star Trek universe, was established under Coon's tenure on the series; the Klingons were introduced ("Errand of Mercy"), the galactic governing body United Federation of Planets was named ("Arena"), Starfleet Command was firmly established as the USS Enterprise's operating authority ("Court Martial"), and the Prime Directive was first articulated ("The Return of the Archons"), as well as introducing Zefram Cochrane ("Metamorphosis"), Khan Noonien Singh, and the Augments ("Space Seed"). James T. Kirk actor, William Shatner, has flat-out attributed the creation of all of these to Coon in his book Star Trek Memories (1995, p. 219).
Besides writing and producing the series, Coon often did uncredited rewrites on the scripts, just like he did in The Wild Wild West. (The Star Trek Compendium) He was also known for his ability to write scripts in a very short time. For example, Coon wrote "The Devil in the Dark" over the course of four days. (The World of Star Trek)
Coon left the series mid-season 2, partly because of being tired and worn-out by the constantly exhausting work, and partly because of his dispute with Roddenberry, who disliked the more light-hearted, comedic approach taken by the show under Coon's guidance (especially the three straight-out comedy episodes, "I, Mudd", "The Trouble with Tribbles", and "A Piece of the Action"). Despite leaving the series as producer and head writer, Coon continued writing for Star Trek, using his pseudonym "Lee Cronin". (Inside Star Trek: The Real Story, These Are the Voyages: TOS Season Two) For all Coon's positive contributions, one of his later episodes, "Spock's Brain", ironically turned out to be one of the least, if not the least, appreciated Original Series episodes.
Coon was invited, by D.C. Fontana, to write for Star Trek: The Animated Series but declined her offer, being uninterested in it. As such, he was one of only a few people who turned down the invite. (Star Trek: The Magazine Volume 1, Issue 16, p. 67) Nevertheless, in his stead he suggested his friend and last student/protegé, Russell Bates, which turned out to be an inspired suggestion, as his episode "How Sharper Than a Serpent's Tooth" won the sole Emmy Award either Original Crew television series had won. In a short 2008 vidcast interview, given for Larry Nemecek's TrekLand blog, Bates related that his Emmy-winning episode had been a subtle homage to what Bates believed to be his mentor's Original Series' episode "Who Mourns for Adonais?". Bates was only partially wrong in his beliefs, as that episode, while not conceived by Coon, was heavily revised by him for it to become the episode as ultimately featured. 
Gene Coon already died in 1973, before witnessing for himself the spectacular resurgence in syndication of the series he so much helped to take shape. Had he lived, Coon might have come to regret the glowing praise he had for Roddenberry back in 1968, as Roddenberry himself had never been able to bring himself to return the compliment, and worse. As it turned out, Coon himself had not been able to counteract Roddenberry's "revisionist" (typified as such by former colleague David Gerrold in the 2014 documentary William Shatner Presents: Chaos on the Bridge) absconding of his contributions during the latter's vigorous Star Trek convention and lecture campaigning during the entire 1970s and early 1980s, more or less claiming Coon's contributions to Star Trek as his own, after Roddenberry had belatedly realized that his contributions were among the most popular for Star Trek, and which had made the second season so beloved in the first place. By consistently keeping Coon's name under wraps all this time, Roddenberry nearly succeeded in relegating Coon to oblivion, were it not for others, who had worked closely with Coon at the time, like Shatner, Herb Solow, and Justman, who were of a different mind, refusing to let Roddenberry get away with it, in such writings as Star Trek Memories (dedicating an entire chapter to him, significantly entitled, "The Unsung Hero"), and Inside Star Trek: The Real Story. In the latter book (1997, p. 430), Solow has summarized this state of affairs as follows, "My displeasure grew over the years as he reinvented the origins of Star Trek, further enlarging the Star Trek legend and the Gene Roddenberry myth. While there is no denying that Gene created the root, the core from which the series grew, there were other important contributors to its growth: Gene Coon, Bob Justman, Matt Jefferies, and me [also including Leonard Nimoy's portrayal of Spock, the "brightest of all stars in the Star Trek universe", according to Solow]. Unfortunately, the credit for our contributions was washed away in the wake of Gene's disinclination to honor them, and by doing so, he assumed their authorship."
Though both books were published after Roddenberry's death, Shatner actually took it up a notch while the "Great Bird of the Galaxy" was still alive. Even though he had not nearly as large a bone to pick with Roddenberry as, for example, his co-star Leonard Nimoy had, Shatner apparently felt damned if he would let Roddenberry get away with the perceived injustice. On 6 June 1991 shortly before celebrating the 100th episode of Star Trek: The Next Generation, the Producers Building at the former Desilu studio lot was renamed "Gene Roddenberry Building", and Shatner was one of the speakers at the dedication ceremony. During his speech, Shatner purposely dropped Coon's name a few times, in an effort to embarrass Roddenberry. Very shortly after Roddenberry's death five months later, Shatner, not in the slightest rueful, explained himself, "In my opinion, Gene Coon had more to do with the infusion of life into Star Trek than any other single person. Gene Roddenberry's instincts for creating the original package are unparalleled. He put it together, hired the people and the concept was his and set in motion by him, but after 13 shows other people took over. Gene Coon spent a year and set the tenor of the show and there were several other producers who were writer/producers who defined its character. Gene [Roddenberry] was more in the background as other people actively took over." (Cinefantastique, Vol 22 #5, p. 39) Shatner in particular, has not let the issue slide, nor did he mellow over time, when he, as late as 2008, wrote in even harsher tone in his Up Till Now autobiography, "After the first thirteen episodes writer/producer Gene Coon was brought in and Roddenberry became the executive producer, meaning he was more of a supervisor than working on the show day -to-day. After that his primary job seemed to be exploiting Star Trek in every possible way." 
Others have come to agree (in principle) with Shatner and company, as Coon has been endowed with meaningful monikers like "The Other Gene" (Star Trek Magazine issue 125; ), "The Half of Star Trek's Genes" (By Fontana ), and specifically, "The Forgotten Gene", popularized by Mark A. Altman and Robert Meyer Burnett, who had the sobriquet prominently featured in the credit roll of their popular 1998 Star Trek inspired comedy/parody, Free Enterprise (which featured Shatner), all of them ensuring that Coon's Star Trek legacy is currently not "forgotten".
Career outside Star Trek
The eldest son of US Army Sgt. Merle Jack "Pug" Coon and decorator Erma Gay Noakes, Eugene Lee Coon was born in Beatrice, Nebraska, on January 7, 1924. At four years of age, he showed talent, singing on the radio at WOAW AM in Omaha. He knew twenty-four songs, including one in French and one in German. As his boyhood went on, he was a member of the Gage County 4-H Club and the Boy Scouts of America. He later attended Omaha Technical High School and participated in Junior Reserve Officers' Training Corps (JROTC), also playing in the school band. During this time, he was also a teenage newscaster for KWBE AM in Beatrice. He later moved, with his parents and younger brothers, Merle Jack Coon, Jr. and Bloise Newell Coon, to Glendale, California. Another brother died at ten years old when they still lived in Beatrice. His father found employment there working with poultry, and Coon transferred to Glendale High School.
During World War II, Coon served stateside in the United States Marine Corps from 1942 to 1946. Thereafter, he remained in the Marines as a reservist while studying radio communications at Glendale Junior College, where he performed in a production of The Night of January 16th. Coon attended and, in 1948, graduated from, the Frederich H. Speare Professional School of Radio Broadcasting in Hollywood, California. Coon's former protégé Russell Bates has, in 2008, filled in some additional details on Coon's earlier life, which had hitherto been unknown. He possibly met Gene Roddenberry as he worked on several television productions such as Dragnet in the late 1950s and early 1960s, among others Have Gun – Will Travel and The Lieutenant.  Following additional studies at the University of Iowa, he returned to active duty during the Korean War in 1950. He received additional training as a war reporter as well as running a pharmacy and building houses. He wrote about many of his experiences in the novels Meanwhile Back At The Front and The Short End of the Stick.
Upon his demobilization in 1952, Coon found work first as a radio newscaster before turning to freelance writing under the mentorship of Los Angeles Times reporter Gene Sherman. He also covered atomic bomb tests in Las Vegas, including Operation Big Shot. From 1954 to 1959, he operated a pharmacy at the intersection of Beverly Boulevard and North Ardmore Avenue; during this period, Sherman covered his pharmacy exploits in Page 2 Cityside column for the newspaper. Sherman also allowed Coon to have a guest spot promoting Meanwhile Back at the Front in the column he (Sherman) wrote for The Farmer's Market, using the pen name "Dick Kidson." Beginning in 1956, Coon was primarily involved in scripting teleplays for popular western and action television shows, including Dragnet (1951), Wagon Train (1957), Maverick (1957), and Bonanza (1959). At Universal in the early 1960s, he turned McHale's Navy (1962) from a one-hour drama into a successful thirty-minute sitcom. Together with the writer Les Colodny, Coon floated the idea for The Munsters (1964), as a satirical spin-off from The Donna Reed Show (1958), to MCA chairman Lew Wasserman. The result of this last, whose format was worked out by Allan Burns and Chris Hayward and whose characters and situations were developed by Norm Liebman and Ed Haas, was yet another hit show. MCA, then the parent company of Universal Studios, produced the show through its Revue TV and Kayro-Vue Productions banners.
In 1957 he wrote two films for Universal Pictures, The Girl in the Kremlin and Man in the Shadow. Both films featured William Schallert in the cast, while the latter co-starred Orson Welles and also featured Paul Fix. He also wrote the script for the 1964 film The Killers (featuring Seymour Cassel) – best known for being Ronald Reagan's final acting role before entering politics. Coon began to write for television in the late 1950s. Among his many contributions, he wrote two episodes of Zorro, both of them featuring Ken Lynch, an episode of My Favorite Martian (starring Ray Walston), and an episode of Have Gun – Will Travel, on which Gene Roddenberry served as one of the leading writers. He also wrote an episode of Bonanza which featured Leonard Nimoy and another episode which featured Michael Forest and Anthony Caruso.
Following his tenure on Star Trek, Coon produced the series It Takes a Thief, which co-starred Malachi Throne. Novice writer Glenn A. Larson served on the series, and Coon took him on as an apprentice, helping him develop the story line of Adama's Ark, which evolved into the classic Battlestar Galactica science fiction series a decade later. Larson, whose creation evolved into a full-fledged franchise of its own over time, was grateful for "Coon's perception of science fiction".  He also wrote an episode of The Sixth Sense featuring William Shatner, and two episodes of the Harve Bennett-produced The Mod Squad, starring Tige Andrews and Clarence Williams III, and directed by Lawrence Dobkin. With Gene Roddenberry, Coon wrote The Questor Tapes, an unsold 1974 pilot which was directed by Richard Colla and featured Majel Barrett and Walter Koenig; Robert Foxworth played the title character. Data, the android from The Next Generation, was based on Questor. Though the series was not picked up, it did earn him, posthumously, and Roddenberry a 1975 Hugo Award nomination in the category Best Dramatic Presentation. Coon died before the project was completed, and D.C. Fontana's novelization of the pilot is dedicated to his memory.
Coon divorced his first wife, Joy, in 1968, and married his radio school sweetheart, model-actress Jacqueline Mitchell. Joy died one year later of cancer, and refused to allow her ex-husband to visit her in the hospital. Coon was shattered by the event. (Inside Star Trek: The Real Story, pp. 347-349, 428) Coon, a chain smoker of cigarillos, died of lung cancer in 1973, only a week after being diagnosed. He visited Robert Justman's office one day, wearing a portable oxygen tank and mask, gasping and coughing. Justman urged him to go in for medical tests, despite the fact that Coon said his breathing difficulties stemmed from the "Goddamned LA smog." (Inside Star Trek: The Real Story, pp. 428-429)
A young writer named Justin Murphy wrote and self-published the book Gene L. Coon: The Unsung Hero of Star Trek, taking his cue from Shatner's similarly titled autobiography chapter. Chronicling his early upbringing in Beatrice, Nebraska and adolescence in Glendale, California. Along with his early careers as a pharmacist and freelance reporter before his eventual screenwriting career and stint on Star Trek. It is available on Amazon Kindle. The audio version is available through Amazon.com, Audible.com, and iTunes, narrated by Star Trek actor and lifelong fan Jack Nolan. On the weekend of, March 2-4, 2018, there was an event honoring Gene L. Coon in his hometown of Beatrice, Nebraska.
Star Trek credits
- Writing / co-writing credits
- TOS, as Gene L. Coon:
- TOS, as Lee Cronin:
- Producing credits
Emmy Award nomination
As Producer, Coon received the following Emmy Award nomination in the category Outstanding Dramatic Series: