Cain

When the first human spirits flickered into awareness in The Dreaming, Cain and his brother Abel manifested as ideologues of the spirit of humanity itself. They competed for the Creator's affection. Miserly and jealous, Cain struck Abel with the jaw of an ass, and slew him. Cain was branded the First Murderer. For this, he was banished to Hell. He rose up to become a Knight of Hell, a member of the peerage of hellions. Bearing the Mark of Cain, he was one of the most fearsome supernatural warriors in Creation.

When Merlyn capped the hole in reality caused by Morgana Le Fay, he installed the House of Mystery to maintain it. Cain was chosen to guard the House as his eternal penance.