Jean Claude Magnum is a Hollywood actor who has starred in several Ninja Movies. He is the suitor and opponent of Mai Kujaku, who challenged her to a duel for the right to marry her. He attempted to use Hollywood trickery to briefly kidnap Mai after he lost to her. His name is a reference to actor Jean-Claude Van Damme. In episode 80, it is revealed that he already has won 5 Locator Cards and if he won the duel against Mai, not only would he marry her, but also take her place in the Battle City Finals.
Magnum uses a Ninja Deck composed of low-level Ninja monsters, many of whom Special Summon other monsters when they are Summoned.