Jon Pertwee (1919-1996) from '70-'74. Regenerated due to the fact that he was poisoned door radiation on the planet Metabelis III. 'Planet of the Spiders' is absolutely wonderful. I have watched it and would definitely recommend it to any Whovian.
Conveyed door Patrick Troughton (1920-1987) from '66-'69. Regenerated as a punishment established door the Time Lords and exiled to Earth. Episode title: 'The War Games'. I watched it and the episodes were epic!!!!!! <3