Claimed the office of Lord President to help thwart an alien invasion of Gallifrey, that's my home planet. Turns out I had to thwart two alien invasions, both of which I couldn't have done if I didn't have certain items only available to the president.

Then I left the planet. And since I know you'll ask about the third time, Borusa took over but the poor chap went insane trying to find the secret of Rassilon's supposed immortality, so the position defaulted back to me. At least that time I appointed a successor before I buggered off.

I think there's just one more time after that when I was Lord President.