Martin Septim from Oblivion.
In a short amount of time, he goes from a humble monk in a rural town to the emperor of Tamriel. Not only that, but very shortly after that, he is involved in the Battle of Bruma and the Battle of the Imperial City. As an epic cherry on top of the sundae, he also becomes the avatar of the God of Time, Akatosh, and battles Mehrunes Dagon, defeating him and sealing the link between Oblivion and Nirn.
Monk-> Emperor-> Avatar of a God
And he's not even the player character! Thats what I call epic.