John "JNT" Nathan-Turner (born John Turner, 12 August 1947 1 May 2002) was the longest-running producer of Doctor Who, lasting from August 1980 to the end of the original series run in December 1989, overseeing the last season of Tom Baker and the entire tenures of Peter Davison, Colin Baker and Sylvester McCoy.
He got his start on the show in 1969 as part of the floor crew before ascending to production unit manager under Graham Williams in the late 1970s, and ran the show from season 18 (1980) through season 26 (1989). He was a strong proponent of using Continuity Porn, Stunt Casting, and giving his Doctors Limited Wardrobes of Impossibly Tacky Clothes, often as part of an effort to "brand" the programme.
His tenure as producer was very controversial for a number of reasons, mainly for the things listed above. He insisted upon a question mark motif being integrated onto the Doctor's wardrobe, which none of the actors playing the part were happy about. He was also something of a Control Freak, and unlike his predecessors wasn't particularly keen on bringing back previous writers or directors, instead preferring new and inexperienced writers.
Nathan-Turner was also bit a too friendly with the fandom, which resulted in stories that suffered from Continuity Lockout, especially in era before home video or steaming (contrast this with Jon Pertwee-era script editor Terrance Dicks, a thorough believer in Viewers Are Goldfish who emphasized that the audience should never be expected to remember details from an episode that was over two years old). His choice of guest stars was often criticized as they were often light entertainers terribly miscast in their roles, and on one of the rare occasions when he did try snagging a potentially viable guest star— David fucking Bowie of all people— he had to cancel due to a scheduling conflict. Despite this, his first four years were generally well-received, particularly the show's 20th anniversary season in 1983— something Nathan-Turner had done quite a lot to promote. It wasn't until Peter Davison decided to leave that things went horribly wrong.
For the Sixth Doctor, Colin Baker, John Nathan-Turner made very two important but very bad decisions; first he decided to make him a "totally tasteless Doctor" giving him an infamously gaudy multicolored coat that even the actor hated (Baker wanted his Doctor dressed in more tasteful black velvet, which Nathan-Turner thought would look too similar to the getup for Anthony Ainley's version of the Master). The second was that he wanted the new incarnation to be a much darker chap than previous incarnations; it might've worked, for it not for two other things. Rather than take the time to properly develop the Sixth Doctor with his own season, the production staff tagged his debut story onto the end of Davison's last season as a ratings stunt— the result was disastrous as not only did this result in Baker's debut story being horribly rushed, but the new Doctor came off as arrogant, moody, unlikable, and possibly even abusive, especially given the now infamous scene where the Doctor, while suffering from post-regenerative psychosis, nearly strangled his own companion to death; the clown corpse coat just made things worse. Second, Nathan-Turner's insistence on hiring inexperienced writers came to haunt him as they had no idea how to write for the character, resulting in script editor Eric Saward having to extensively rewrite the scripts, causing his relationship with Nathan-Turner to quickly deteriorate. In particular, Saward (unfairly) thought Baker had been miscast and would often sideline the Doctor when he could.
The results were disastrous. Viewing figures took a nose-dive and the show was involuntarily put on a 18 month hiatus at the order of BBC1 Controller, Michael Grade (who hated the show and wanted it canned). Baker had another disastrous second season after the original plans were thrown out at the last minute in favor of an arbitrary story arc featuring the Doctor (and, metaphorically, the show) being put on trial. Eric Saward had finally had enough and quit with one episode to go, causing utter chaos both on-screen and off, Baker was unfairly scapegoated for the show's problems, and he was unceremoniously fired, giving him the unfortunate distinction of being the only actor to be outright axed from the role of the Doctor (despite this, he still loves Doctor Who dearly and was even made President of the Doctor Who Appreciation Society).
Nathan-Turner, naturally, had actually wanted to leave the show by this point, but he was forced to stay on as nobody else wanted to sit at the helm of a rapidly sinking ship; he mainly became concerned with just keeping things going, and took a much more laissez-faire approach to the show from this point onward while new script editor Andrew Cartmel became the driving creative force for the classic run's last years. The show limped on for three more seasons before unceremoniously and ignobly fizzling out in 1989; even though Cartmel was trying and succeeding to breathe new life into the show (and we should emphasize the "succeeding" part; fans feel that his tenure as script editor marked the last creative high point of the original 26-year run of Doctor Who), the damage had been done, not helped by the BBC executives deliberately tanking the ratings by scheduling the series against ITV's flagship Prime Time Soap Coronation Street. It wouldn't be until 2005 that Russell T. Davies would bring the show back to massive popular and critical acclaim, under the new title of "head writer" (by this point the "producer" role had become much less consequential for the direction of the series).
In later years, Nathan-Turner was responsible for the direction of the home-video releases of Doctor Who, and produced some of the earliest of the show's bonus features in the form of short documentaries on specific Doctors and villains. Nathan-Turner's work at maintaining a home series presence for the show arguably helped keep the fandom alive during the 16-year interim by ensuring that there would always be a way to access and discuss it, though it didn't do much to save his reputation among said fandom, who still view him as something of a pariah who just wasn't capable of handling a show like Doctor Who and eventually trapped himself into it as a result. Of course, this reputation isn't totally undeserved given everything mentioned above, though it does occasionally dip into the realm of implying that Nathan-Turner never did anything good for the series despite plenty of evidence to the contrary.
Always known for liking a drink, this ultimately developed into full-blown alcoholism, leading to his health failing in his waning years; he died of an infection at the age of 54 in 2002, just a year before the announcement that Doctor Who had been revived.
On a more trivial note, Nathan-Turner was the first openly gay creative director for the series; his partner, Gary Downie, was a fellow co-worker at the BBC and ultimately became BBC Television's production manager. Doctor Who wouldn't have another heterosexual creative director until Steven Moffat took on the position in 2010, thirty years after Nathan-Turner was first given the reins.