Marcel Bonaparte, known in Japan as Martin Kanou, is a new student entering Ra Yellow in the third season. Through Yubel's possession he acts as the main antagonist for the second arc of the season.
Noteworthy for looking very pale and sickly, he is close friends with Blair Flannigan. After being transported to the Realm of the Beasts, Marcel is corrupted by the mysterious Devil Arm possessing Yubel's spirit, the mysterious demon that Thelonious Viper was helping. He then turns many students and faculty members into Duel Ghouls and plans to unleash the Sacred Beasts before declaring himself king of his newly-instituted empire.
Marcel is Jean-Louis Bonaparte's son, raised by the man's ex-wife, Joséphine. He grew depressed by the sight of his parents bickering and his father leaving their home in Paris at a young age (in the dub, Marcel missed his father and there was no divorce). It is this depression which allows Yubel to possess him. During his possession, Marcel has expressed a desire for the company of others, this being another reason why he turned students and faculty into Duel Ghouls.
During the Duel with Jaden Yuki and Jesse Anderson, Marcel is set free from the creature's influence when Yubel regains physical form. After Duel Academy is restored to its proper place, Marcel recuperates but not before being checked on by Blair while Bonaparte apologizes for making him depressed in the first place. However, Marcel will never forget the pain and suffering Yubel put on him.
Marcel is seen one more time prior to when the Duel Academy students go to see if everybody made it back.
He leaves the academy in the fourth season to spend more time with his father.
Marcel speaks in a French accent in the English dub, except for when he is possessed by Yubel. When he speaks without his accent, it is actually Yubel speaking through him. (This causes sort of a "running gag" in the dub, where everyone who he speaks to asks him "What happened to your accent?") This incarnate of her is akin to a split personality for Marcel, as it refers to itself as "your best friend" when consoling Marcel when he thought he had no friends. Occasionally, his voice gained the same vocal effect Yubel's did, and he sometimes used her voice (at which time he glowed blue in the dub). In the original version, Yubel used her own voice when she possessed Marcel more often, and Marcel's body didn't glow blue when he used his own voice.
Marcel plays two Decks while possessed by Yubel. The first is an Exodia Deck. By using cards such as "Mad Reloader" and "Break the Seal", he is able to quickly gather the individual pieces of Exodia and declare an automatic victory. The second Deck is a Sacred Beast Deck. He boosts the Summoning speed of the "Sacred Beasts": and also supports the Summoning of their combined form, "Chaos Phantasm Armityle". These cards were only used when he was possessed by Yubel, so it's unknown if the Exodia Deck was his or one made by Yubel.