4. He Got Everything Done In One Season
I will admit right away that Eccleston only has one season and he maybe is not as fleshed out as some of the other Doctors. Both Colin Baker and Sylvester McCoy said before the show was cancelled how they would have made the Doctor more complex or brought something new and that their time was unceremoniously cut short. Eccleston controversially left the show because of behind the scenes politics but his lone season provides a complete character arc for him to go through. From the start the Doctor is alone and a war survivor. He finds Rose, takes her on his travels and slowly they develop, admittedly uneasy, feelings for each other. Through facing danger together these feelings grow until in the Dalek-laden finale Rose saves the Doctor (and the Earth, just for good measure) before the Doctor sacrifices himself to save her. Some Doctors embraced death, knowing that the next incarnation could be a radical change. Some went out fighting it, like Patrick Troughton or David Tennant, but only Eccleston ends on a complete character change that climaxes in his accepted regenration.