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 he created to take control of 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 shoots a blue ball that splits in two when touches the floor, each part sliding a different direction. When the machine is destroyed, he flies out from it and reveals that he is really 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