Originally Posted by JQ
Kuan-Yen Xorn and Shen Xorn were twin brothers from China, both mutants, one with the power of a star in his head, one the power of a black hole. Kuan-Yen Xorn came under the influence of as-yet-to-be-revealed entity that forced him to assume the identity of Magneto, battle the X-Men and destroy Manhattan. He was subsequently killed by Wolverine near the end of that battle, in the Planet X storyline.
Soon thereafter, his twin brother Shen surfaced and briefly joined the X-Men. This Xorn brother was de-powered during M-Day.
Because Xorn's powers were psychokinetic, and his personality was so strong, it basically remained an almost disembodied sentient thing among the big ball of mutant energy. When that energy got sucked down to Earth by Michael and all absorbed by him, Xorn was the dominant personality in the mix, and that's what drove him towards Genosha and Magneto.