(written from a Production point of view)
John D.F. Black began his writing career in the late 1950s with the horror film The Unearthly (1957, featuring Arthur Batanides). After that, he worked on several television shows. In 1964, he won a Writer's Guild award for an episode of the television series Mr. Novak (in which Walter Koenig incidentally guested). Gene Roddenberry invited him to visit his home following the ceremony, a kind of impromptu audition that turned into a job offer. Black served as the first Executive Story Consultant, and also worked as an Associate Producer (along with the more famous Robert Justman). He met his future wife, then Mary Stowell, while working there.
His writing contribution to Star Trek: The Original Series was limited to a single episode, "The Naked Time", that was later reprised as an episode of Star Trek: The Next Generation. He once said the hardest part of his supervisory job was dealing evenhandedly with writers – both those who intimidated him, like Theodore Sturgeon, and those he felt weren't living up to the show's standards. Black left the series when he got a big-money contract from Universal Pictures. The last episode he worked on was "Miri".
Black was mainly responsible for the famous opening speech for The Original Series, which was developed by him and Justman from Roddenberry's original idea. (Inside Star Trek - The Real Story)
According to Justman and Herb Solow's book, Inside Star Trek: The Real Story, Black didn't get along well with Roddenberry. A week after he finished the script for "The Naked Time", Black discovered that Roddenberry rewrote it, without consulting with him, or even telling him about it. Black was disappointed and never again had the same positive disposition for the series. When he left the show, he celebrated the fact that he no longer worked for Roddenberry. (Inside Star Trek: The Real Story, p 139)
Black also wrote the original "envelope" script for "The Menagerie, Part I" and "The Menagerie, Part II". However, Roddenberry completely rewrote it and took sole onscreen credit for the two-parter. Black filed a Writers' Guild grievance over payment and screen credit, but his claims were denied. (Inside Star Trek: The Real Story, p 251)
Following his tenure on Star Trek, he continued working as a writer and producer until about 1978, returning only three times after that: to collaborate on two Next Generation episodes, an episode of Hell Town (featuring Jeff Corey) and an episode of Murder, She Wrote. The time repeated itself when Black left the production of The Next Generation. Black questioned some rewrite instructions from Gene Roddenberry for the episode "Justice" and was asked to leave. Worley Thorne took over and rewrote "Justice". (Creating the Next Generation: The Conception and Creation of a Phenomenon, p. 46)
In a 2006 review of "The Naked Now", Wil Wheaton complained about the lines Black provided for his character Wesley Crusher: "In fact, John D.F. Black – who I didn't realize at the time hated me – also wrote "Justice", where he gave me the awesome line, "We're from Starfleet! We don't lie!" Thanks for that one, too, Mr. Black."  In fact, Black got screen credit for "The Naked Now" only for his story, originally pitched for The Original Series, dated 12 May 1967 on which the episode was based. 
- TOS: "The Naked Time" (written by)