Mutant Master

Mutant Master was a Marvel comics super-villain and enemy of the X-Men, originally believed to be a powerful mutant he was revealed to be an alien known as a Siris and was posing as an Earth mutant with the hopes of sparking World War III, wiping out humanity so his own kind could take over.

In order to assist in his sinister goals he formed the short-lived terrorist group known as Factor Three, who also clashed with the X-Men.

Ultimately he would commit suicide after his many pawns turned on him, realizing he was not a mutant but instead a bloodthirsty alien intent on global genocide.