Jon Pertwee, as The Third Doctor, played a Doctor who was exiled to Earth by the Time Lords. For his efforts of righting wrongs etc, which one could also describe as interference, the Time Lords thought it best to disable the TARDIS and maroon the Doctor in modern-day London. This was the golden era of The Doctor working for U.N.I.T. and the relationship with The Brigadeer. Oh, and The Master, because of course The Doctor needed an arch nemesis.

Doctor Who Season 7 - 1970

This season began with The Doctor landing the TARDIS deep in some woods, and falling out the front door in a coma only to end up in a country hospital. In the meantime there was a crisis with things falling out of the sky and people being killed in strange ways. The story ended up introducing the Nestenes, a consciousness from outer space that inhabits plastics.

Doctor Who Season 8 - 1971

Doctor Who Season 9 -- 1972

Doctor Who Season 10 -- 1972-1973

This season marks the point where The Doctor was released from exile to Earth. In The Three Doctors, the Doctor performed a great service for the Time Lords by stopping the attack on their home world by Omega. At the end of the episode arc, the Time Lords sent a new dematerialization circuit, and restored the memory of time travel.

The season ended with the farewell of Jo Grant.

Doctor Who: The Three Doctors, William Hartnell, Patrick Troughton, and Jon Pertwee In this, the first multi-Doctor story, we see a situation so dire that the Time Lords must bring together multiple incarnations of The Doctor. The name Gallifrey had not been revealed yet, but the Time Lords "home world" was under attack by Omega. Omega was the Time Lord who developed the time experiments which gave Time Lords the ability to travel throughout time. However in the process Omega was trapped in an alternate dimension, and sought revenge.