The Third Doctor is the third incarnation of the protagonist

Doctor (Doctor Who)

The Doctor is the central character in the long-running BBC television science-fiction series Doctor Who, and has also featured in two cinema feature films, a vast range of spin-off novels, audio dramas and comic strips connected to the series....

 of the long-running BBC

BBC

The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 television science-fiction

Science fiction on television

Science fiction first appeared on a television program during the Golden Age of Science Fiction. Special effects and other production techniques allow creators to present a living visual image of an imaginary world not limited by the constraints of reality; this makes television an excellent medium...

 series Doctor Who

Doctor Who

Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

. He was portrayed by actor Jon Pertwee

Jon Pertwee

John Devon Roland Pertwee , was an English actor. Pertwee is best known for his role in the BBC science fiction television series Doctor Who, in which he played the third incarnation of the Doctor from 1970 to 1974, and as the title character in the series Worzel Gummidge...

.

Within the series' narrative, the Doctor is a centuries-old Time Lord alien from the planet Gallifrey

Gallifrey

Gallifrey is a fictional planet in the long-running British science fiction television series Doctor Who and is the homeworld of the Doctor and the Time Lords...

 who travels in time and space in his TARDIS

TARDIS

The TARDISGenerally, TARDIS is written in all upper case letters—this convention was popularised by the Target novelisations of the 1970s...

, frequently with companions. When the Doctor is critically injured, his body automatically regenerates; as a result, his physical appearance and personality change.
The Third Doctor was a suave, dapper, technologically-oriented, and authoritative man of action, who not only practised Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

ian Aikido

Aikido

is a Japanese martial art developed by Morihei Ueshiba as a synthesis of his martial studies, philosophy, and religious beliefs. Aikido is often translated as "the Way of unifying life energy" or as "the Way of harmonious spirit." Ueshiba's goal was to create an art that practitioners could use to...

 (or Karate

Karate

is a martial art developed in the Ryukyu Islands in what is now Okinawa, Japan. It was developed from indigenous fighting methods called and Chinese kenpō. Karate is a striking art using punching, kicking, knee and elbow strikes, and open-handed techniques such as knife-hands. Grappling, locks,...

), but enjoyed working on gadgets and riding all manner of vehicles, such as the Whomobile and his pride and joy, the canary-yellow vintage roadster nicknamed "Bessie," a construct which featured such modifications as a remote control, dramatically increased speed capabilities and even inertial dampeners.

While this incarnation spent most of his time exiled on Earth, where he grudgingly worked as UNIT

UNIT

UNIT is a fictional military organisation from the British science fiction television series Doctor Who, Torchwood and The Sarah Jane Adventures...

's scientific advisor, he would occasionally be sent on covert missions by the Time Lords, where he would often act as a reluctant mediator.