Troughton's Doctor was an outwardly scruffy, light hearted and bumbling tramp, a portrayal that was nicknamed the Cosmic Hobo.

His original Swinging Sixties companions were the sophisticated socialite Polly (Anneke Wills) and working class sailor Ben Jackson (Michael Craze), who had travelled with his previous incarnation.

Following Ben and Polly's departures, the Doctor and Jamie were joined by the Victorian orphan Victoria Waterfield (Deborah Watling) and 21st century astrophysicist Zoe Heriot (Wendy Padbury).

The First Doctor grew progressively weaker while battling the Cybermen during the events of The Tenth Planet (1966) and eventually collapsed, seemingly from old age.

Although she felt great affection for the Doctor and Jamie, she was never able to completely come to terms with life in the TARDIS and the constant danger that resulted.

During his second incarnation, the Doctor confronted familiar foes such as the Daleks and the Cybermen, as well as new enemies such as the Great Intelligence and the Ice Warriors.

[2] Following the defeat of the Great Intelligence, Lethbridge-Stewart was promoted to Brigadier and became the leader of the British contingent of UNIT, a military organisation tasked to investigate and defend the world from extraterrestrial threats.

In his final story The War Games (1969), the Second Doctor's time came to an end when the TARDIS landed in the middle of a warzone, created by a race of alien warlords who, with the help of another renegade Time Lord the War Chief, progressively kidnapped and brainwashed humans into becoming soldiers for them, hoping to use the ones who survived to conquer the Galaxy.

Although the Doctor was able to defeat their plan, he realised he would be unable to return the human subjects to their various original points in Earth's history.

He therefore contacted the Time Lords, sacrificing his own freedom in the process, and despite an attempt to escape was forced to return to his home planet.

According to this theory the Time Lords used the Second Doctor as an agent after the events of The War Games (1969), and that he did not in fact immediately regenerate and enter his exile on Earth.

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 to have others underestimate his true abilities.

In The Enemy of the World (1968) while impersonating villain Salamander who is his doppelganger, he interrogates Jamie and Victoria without their knowing that it is really himself, provoking them until they nearly physically attack him.

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.

[10] In stories set in colder environments, Troughton wore a cloak (The Highlanders, The Tomb of the Cybermen) or a short fur coat (The Abominable Snowmen, "The Five Doctors").

He is seen piloting the TARDIS and acting in unison with twelve other incarnations of the Doctor to save Gallifrey on the final day of the Time War.

Troughton received a mixed reception from viewers at first; letters sent to the Radio Times both praised "the superb character he has created" and criticised "a wonderful series" for turning into "what looked like Coco the Clown".