Mr. X

Mr. X could refer to:
 * Go Shijima - Kamen Rider Mach, who used this alias to aid the Special Investigations Unit while being under the assumption of being brainwashed by the Roidmudes.
 * Tenjuro Banno - Kamen Rider Gold Drive, who used this alias to lure the Kamen Riders and the Roidmude generals into a trap to power the Sigma Circular at the same time of destroying his creations and the Riders by having Roidmude 004 self-destruct.