Molag Bal

Molag Bal is the Daedric Prince of Rape, Domination and the Enslavement of Mortals. He is the main antagonist, and is attempting to pull Tamriel into his realm of Oblivion, Coldharbour, in an event known as the Planemeld. Molag Bal has stolen the soul of the player, forbidding them to die. To reclaim your soul, you must save Tamriel from the Prince's clutches.

Source: uesp.net.