Brron, Mad King of Dark World serves as the first main antagonist of the Dark World arc of season three. He makes his first actual appearance in episode 135 when Jaden travels to his stronghold.
Demented and sadistic, Brron rules the alternate dimension as its vile dictator. Although his role in the anime is brief, his actions are vital in Jaden Yuki's transformation into the Supreme King of the alternate dimension.
Being the leader of the Dark World creatures, Brron was responsible for the deplorable state of the second alternate dimension and oppression of its denizens. His right-hand man, Zure, oversaw Brron's will, detaining anyone who defied him in internment camps while killing duelists who could be threats to him. The executions occurred at his fortress and involved releasing monsters at disarmed duelists while Brron himself and his minions watched the spectacle. After learning of Jaden's presence in his domain, Brron orchestrated a plot that involved turning Jaden evil.
Due to an underhanded maneuver by his top subordinate, Zure, Brron had a clear advantage with his set of "Wicked Doctrine" cards because should one of them be activated one of Jaden's friends would be sacrificed. Eventually, Jaden defeated Brron in a fit of rage, but not before Alexis, Chazz, Atticus and Tyranno were all sacrificed. Only Syrus managed to avoid that fate. After his defeat, Brron mocked Jaden by saying that he would never see his friends again before dying. It was later revealed that Brron was simply one of Yubel's pawns, who used him to complete the integral part for her plan, the creation of the "Super Polymerization" card, and to simultaneously coax Jaden towards his descent into darkness (although it isn't stated how the two of them ever met, if they met at all).
Brron plays a Dark World Deck, evil creatures whose latent abilities are activated when they are discarded by a card effect. He mainly focused on the gathering of the Wicked Doctrine cards which grants Brron access to his most powerful monster, Colorless, Chaos King of Dark World, summoned through the card, "Super Polymerization", although the Colorless card is not actually seen due to the fact that Brron could not offer Syrus through Wicked Rune - Doubt. If the aforementioned strategy fails, Brron focuses on the summoning and preservation of "Reign-Beaux, Overlord of Dark World", which has the ability to destroy his opponent's Monster cards or Spell and Trap cards.