Mr. X

Mister X is basically a fake name of Dr. Wily, which he used to mask his true identity in Mega Man 6. Mr. X is a billionaire that sponsored the 1st Annual Robot Tournament, that was created by him to take control from eight of the strongest Robot Masters in the final event of the tournament and conquer the world.

He fights with a machine called X Crusher that swings in the screen and shots a blue ball that splits in two when touches the floor and each part slides through a direction of the floor. When the machine is destroyed, he flies out from it and reveals that he is in reality Dr. Wily, before escaping to his fortress.

Trivia
Just before unmasking himself, Mr.X cries out: "My plan for world domination has faild". This typo was fixed in the Mega Man: Anniversary Collection