The Third Doctor Who
The third Doctor was played by Jon Pertwee, who began life after the second doctor was found guilty of breaking the laws of non-interference by the Time Lords. As a result, the third Doctor began in exile on 20th Century Earth.
The Doctor quickly made arrangements with UNIT to serve as their "Scientific Adviser" in return for facilities to repair the TARDIS.
The arrival of the Master changed things and the Time Lords allowed the Doctor limited use of the TARDIS with the condition it was always returned to 20th century earth upon completion of a mission.
The Time Lords eventually restored full knowledge of the TARDIS and lifted his exile after successfully stopping Omega from destroying the Time Lords.
This incarnation of the Doctor was again different than the predecessors, being more a man of action, unafraid to pitch in with his physical skills and often using his Venusian Aikido skills when called for. He also showed a great passion for gadgets and as he spent a lot of time on 20th Century Earth, he was especially fond of his vintage car Bessie and his futuristic Whomobile.
As a man of action, he had little patience for bureaucracy and authority figures and was the first Doctor to consume alcohol.
The Third Doctor finally died and regenerated into the fourth Doctor by exposing himself to lethal levels of radiation in order to defeat the Spiders of Metebelis III.