Patrick Troughton played the second incarnation of the Doctor,and his first companions were Polly (Anneke Wills) and Ben (Michael Craze). This incarnation was more akin to Charlie Chaplin than Hartnell's Doctor, who I think is rather like a doddery Shakespearean actor, but anyway...
In Hartnell's run, they introduced monsters like the Daleks and Cybermen, but in Troughton's Era, they introduced monsters like the Ice Warriors, Krotons, and the Time Lords themselves. In the end, Patrick Troughton's Doctor was exiled,and forced to regenerate into a new form, ending one way of Time Lord, and giving rise to another.