At a person level, the First Doctor has ended two tales abnormally unhappily - turning an complete earth into a wasteland, committing a genocide towards just about every Dalek there, and observing two of his companions get Killed Off for Real at the stop of "The Daleks' Master Plan" and intentionally choosing not to support avert thousands of innocent folks from getting slaughtered by spiritual maniacs at the end of "The Massacre".