Madelyne Pryor is a clone of Jean Grey created by Mr. Sinister to infiltrate the X-Men. She is currently preparing to make her move and set Sinister's plan in motion.
Madelyne "Maddy" Jennifer Pryor is a clone created by Mr. Sinister with a lock of Jean's hair. A test-tube baby, she was fully grown in only a few short years. Sinister activated her when she was fully grown and trained her to infiltrate the X-Men. She greatly resents his control over her, but she literally cannot stop herself from obeying him.
Madelyne is preparing to make her move and assume the identity of the currently-incapacitated Jean, and if all else fails, pose as Jean's long-lost twin. Her job is to gain the X-Men's trust as she pulls them apart, and she will not fail.