The combination of David's mutant abilities and mental illness, as well as Farouk's influence, made him a dangerous, unpredictable force, and by the end of season 2, David had become Legion's antagonist rather than its hero. Xavier thought he had vanquished him, but Farouk's essence survived and attached itself to baby David. The Shadow King - real name Amahl Farouk - was a powerful mutant who attempted to lull Xavier into a trap, but he was defeated by the future X-Men leader. The FX series chronicled the life of David Haller, the mutant son of Charles Xavier whose life was thrown off course when he was possessed by the monstrous Shadow King when he was an infant. The Legion ending definitively concludes David Haller's story after three seasons.