If a faction conquerors the Imperial City, its top player is crowned the sole Emperor of Tamriel.
Featuring three-sided Player vs. Player (PvP) gameplay, The Elder Scrolls Online supports hundreds of players on screen at once in an open world fight for control of Cyrodiil. Seize, hold, and control the resources of massive strongholds. Utilize massive siege weapons to crumble fortress walls and smash through fortified gates. Conquer the Imperial City, and your alliance’s top player could even be crowned Emperor!
The Emperor even acquires unique perks and bonuses apprently, though I'm not sure what they are.
Cool tidbit. I can't imagine what the competition is going to be like for that; it would be insanely cool to be the sole Emperor over all of the other players.