After demolishing two races in the Time War, "The Renegade" shed his past and renamed himself "The Doctor." He left to explore the wonders of the universe, helping those in need along the way.
An enigma through and through, the Doctor seems to know everything about everyone, but only a handful of people in the entire universe even know his name. Each generation reveals a different side of the Doctor— it's like he's a different person (wink wink, nudge nudge). Maybe he's the savior of humanity, or maybe he's just a mad man with a box.