Revan, then. If you've played KotOR, you'll know that he's a pretty big deal in that story. And now he's making a return in his very own Star Wars: The Old Republic expansion. Shadows of Revan is its name, and filling the MMO with new story is its game.
Here, have a trailer:
If that appeals, Shadows of Revan is now available to buy for all players. In practical terms it'll offer new story missions, two new planets, an increased level cap, and new Flashpoints and Operations. There's also a new Disciplines system, which rejigs the game's skill trees in order to show players the core of a class's combat much earlier in the game.