Alidar Jarok wrote:
Just based on what Patrick Troughton said, it doesn't even seem clear that any pre-Doctor Doctor left Galifrey. It sounds like he was the first to left and he left because he was bored and because he wanted to help people.
But the Doctor didn't originally have any agenda of helping people. When we first met him, he was an antihero at best, a self-centered and arrogant individual. In "An Unearthly Child," he even attempted to murder a prehistoric human in order to escape and get back to the TARDIS. It was the example set by Ian and Barbara, their determination to help people on their travels, that softened his heart and awoke his potential for activism. (Although by now there are probably a number of novels and short stories that show him as more of a do-gooder before that day in Totters Lane.)