Cyrus Black was a sorcerer who has faced Dr. Strange and the Defenders.
At one point he had control of the Wand of Watoomb, a relic of great power, but lost it to Strange.
He eventually came to the notice of Nightmare, who brought him to his dimension and gave him much greater power than he had had in the past. He used his familiar, a rat named Nebuchadnezzar, to bring Strange to Nightmare's realm, then attacked him. Strange found him to be a formidable foe, but used the light of the Eye of Agamotto to show him his true self--a bitter, pathetic man. Unable to deal with this realization, or perhaps as a means to atone for his actions, he committed suicide, destroying himself instead of Strange.