Kaecilius

Kaecilius is a sorcerer and a former member of the Masters of the Mystic Arts, who became disillusioned with the Ancient One after it refused to allow other dimensions to come to Earth, believing that this would reunite him with his deceased wife and son. He formed the Zealots with the intention of defeating the Ancient One and bringing the interdimensional being known as Dormammu to Earth, but this led him to clash with his former comrades and Stephen Strange. He was defeated and became part of the Dark Dimension for all eternity, earning him the immortality he had long desired.