The Second Doctor (1966 - 1969)
He has been nicknamed the "Cosmic Hobo" as the impish Second Doctor appeared to be far more scruffy and child-like than his first incarnation. The Second Doctor is the first Doctor to put on an act, to hide what he's really thinking, to the point where even his companions are not sure where the act stops and the real Doctor begins. In his first appearance, he claims that his destruction of the Daleks was a complete accident, but in fact it is clear that he had worked out a plan to defeat them much earlier.
Mercurial, clever, and always a few steps ahead of his enemies, at times he could be a calculating schemer who would not only manipulate people for the greater good but act like a bumbling fool in order to have others underestimate his true abilities. Some times, this appears simply as a joke, such as in The Tomb of the Cybermen, where he finishes the archaeologists' calculations behind their backs, but in other times, it seems much darker. In The Evil of the Daleks he coldly manipulates Jamie in trying to rescue Victoria (thus setting in motion the human factor tests) and is unsympathetic when Edward Waterfield tries to apologise for his collaboration with the Daleks. But despite the bluster and tendency to panic when events got out of control, the Second Doctor always acted heroically and morally in his desire to help the oppressed. More than any other perhaps, this incarnation of the Time Lord was a wolf in sheep's clothing.
Patrick George Troughton
(25 March 1920 - 28 March 1987)
In 1966, Doctor Who producer Innes Lloyd decided to replace William Hartnell in the series' lead role. The continued survival of the show depended on audiences accepting another actor in the role, especially given the bold decision that the replacement would not be a Hartnell lookalike or soundalike. Lloyd later stated that Hartnell had approved of the choice, saying, "There's only one man in England who can take over, and that's Patrick Troughton". Lloyd chose Troughton because of his extensive and versatile experience as a character actor. After he was cast, Troughton considered various ways to approach the role, to differentiate his portrayal from Hartnell's amiable-yet-tetchy patriarch. Troughton's early thoughts about how he might play the Doctor included a "tough sea captain" and a piratical figure in blackface and a turban. Doctor Who creator Sydney Newman suggested that the Doctor could be a "cosmic hobo" in the mould of Charlie Chaplin, and this was the interpretation eventually chosen (Howe, Stammers and Walker, 68–69).
During his time on the series, Troughton tended to shun publicity and rarely gave interviews. He told one interviewer, "I think acting is magic. If I tell you all about myself it will spoil it". Years later, he told another interviewer that his greatest concern was that too much publicity would limit his opportunities as a character actor after he left the role.
Troughton was popular with both the production team and his co-stars. Producer Lloyd credited Troughton with a "leading actor's temperament. He was a father figure to the whole company and hence could embrace it and sweep it along with him". Troughton also gained a reputation on set as a practical joker.
Regrettably, many of the early episodes in which Troughton appeared were wiped by the BBC. Troughton found Doctor Who's schedule (at this time, 40 to 44 episodes per season) gruelling, and decided to leave the series in 1969, after three years in the role. This decision was also motivated in part by fear of typecasting. Troughton's decision would eventually become something of an unwritten law (The "Troughton Rule") among actors in order to prevent one from being typecast in a particular role of potentially long-running television programme for more than three years. Patrick Troughton was succeeded in the role by Jon Pertwee.
Troughton returned to Doctor Who three times after he originally left the programme, becoming the only former "Doctor" actor to have reprised the role that many times after his original run. The first time was in The Three Doctors, a 1973 serial celebrating the programme's 10th anniversary. Ten years later, Troughton overcame some reluctance to reprise his role and agreed to appear in the 20th anniversary special The Five Doctors at the request of series producer John Nathan-Turner. He also agreed to attend Doctor Who conventions including the show's 20th Anniversary celebrations at Longleat in 1983. He also appeared around the world with Nathan-Turner. Troughton enjoyed the return to the programme so much that he readily agreed to appear one more time as the Second Doctor with Colin Baker's Sixth Doctor in The Two Doctors (1985). Reportedly, he also advised the Fifth Doctor actor, Peter Davison, to limit his time in the role to three seasons to avoid being typecast and the young actor followed that advice.