William Hartnell, the first Doctor, was pushed rather than jumping from the Tardis. He very much wanted to stay in the role that was beloved by millions and had helped create a massive hit for the BBC. However Hartnell was in his late 50s at the time, and was increasingly erratic and, on occasion, had to miss an episode. Producers took the dramatic, unprecedented (and not to mention, historic) step of replacing their lead actor.
The actor that replaced Hartnell was Patrick Troughton and he , took on the role on the proviso that this was a three-year gig. He's also commented on the fact that, as an actor, he didn't want to be typecast.
Third Doctor Jon Pertwee claimed that he quit the role because of a chronic back problem, but it later emerged that there was an arguement over money with the BBC that provoked him laying down the sonic screwdriver.
Fourth Doctor , Tom Baker handed in his notice every year, but was always lured back by a better deal from the BBC. However when producer John Nathan-Turner came along, attitudes changed. JNT, as he is affectionally known, wanted to bring the show into the futuristic decade that was the '80s. Who got a shiny makeover. A makeover that would see Baker's notice finally accepted.
Fifth Doctor, Peter Davidson took Troughton's advice of not staying longer than three years despite producer John Nathan-Turner asking for him to stay. He did say, however, "It was very demanding, so I was too tired to feel sad when it was all finally over."
Doctor number 6, Colin Baker was effectively sacked from the role when his contract was not renewed although he was asked to come back for four episodes in the following season for his regeneration story. The actor felt more than a little aggrieved and refused the BBC's plans,
"I told them what they could do with their offer. I have been treated shabbily." Colin Baker.
No 7 was Sylvester McCoy - Doctor Who came to an end in 1989 but the show wasn't actually officially cancelled at any stage. McCoy has often lamented the short-sightedness of the BBC given that he and companion Ace (Sophie Aldred) were just hitting their stride. So this entry is an oddity: he didn't leave and he wasn't sacked.He just vanised from the screens.
For one night only, back in 1996, the Withnail & I actor, Paul McGann was most definitely the best thing about the ill-fated Doctor Who TV Movie. But a series didn't follow and fans had to make do with his Big Finish audio dramas.When the show returned, some nine years later, McGann was nowhere to be seen. Not even a regeneration.
Doctor No 9, Christopher Eccleston quit the show after just one season.
He says the relationship with Russell and the producers (which included Julie Gardner, Mal Young and Phil Collinson) broke down "irreparably" at the start of filming and "never recovered".
Eccleston added, "They lost trust in me, and I lost faith and trust and belief in them."
Doctor 10 - David Tennant spectacularly announced his decision to leave Doctor Who live on ITV during the National Television Awards in 2008.Deciding to move on after making the role his own, the Scottish actor didn't want to "outstay" his welcome, saying: "It would be very easy to cling on to the TARDIS console forever and I fear that if I don't take a deep breath and make the decision to move on now, then I simply never will."
Matt Smith, Doctor No 11 simply felt it was time to move on. "When ya gotta go, ya gotta go!" Matt stated in his official leaving statement in 2013.
In an emotional interview on BBC Radio 2, Peter Capaldi announced that he was leaving the show. The Twelfth Doctor said it was "the right time to move on". It now seems that three years has become the norm for an actor to stay in the role.
Doctor Who returns this autum with Jodie Whittaker in the title role.