"Miss Shaw may have the misfortune to work
for you, Brigadier. I am a free agent."

The Third Doctor -- 
Jon Pertwee 

Jon Pertwee's Doctor had a flair for gadgets, vehicles, and frilly clothes. His Doctor was a larger than life hero. A combination of James Bond, Sherlock Holmes and Houdini.

Exiled to Earth in the twentieth century by own his people, the Time Lords, the Doctor becomes the scientific advisor for UNIT (United Nations Intelligence Taskforce). Unable to leave Earth (the Time Lords removed the Doctor's memory of how the TARDIS works) the Doctor is helps UNIT to fight alien invasion and any other terrestrial menace that comes along. However, from time to time, the Time Lords send the Doctor on missions to other worlds, But always he returns to Earth.

After helping the Time Lords defeat Omega, an ancient figure from the Time Lord's past, the Doctor is forgiven and his memory returned to him. But this Doctor is a homebody and he never strays too far from Earth.

The Pertwee Era also introduced the Master, another Time Lord, and the sworn enemy of the Doctor.