Rakanoth, Lord of Despair was a powerful demon.
Rakanoth was originally a servant of Andariel, the Maiden of Anguish. He also served as a warden to the imprisoned angel Izual, whom he guarded in the Plains of Despair - his own 'realm'. He also fought in the Great Conflict, battling Tyrael on at least one occasion.
When Diablo incorporated the essences of the six other Great Evils and became the legendary Prime Evil, he emptied Hell's forces for an assault on the High Heavens. Rakanoth was among those he summoned and was assigned the task of guarding the captured archangel Auriel, holding her in the Library of Fate. However, a group of nephalem rescued the angel and slew Rakanoth.