Brron, the Mad King of Dark World is classified as the first main antagonist in the Dark World arc of Yu-Gi-Oh! GX in season 3.
Brron is a tall, slender humanoid with chains wrapped onto him, and bones for hair.
Brron in the Leader of the Dark World Army. After Zure, his right hand man was defeated by Jaden, Brron challenged Jaden the next day. During the duel Brron mention that Brron captured most Jaden's friends, and that all of them have been marked by a certain symbol. To assure both victory, and to break Jaden's mind he activated 4 Wicked Doctrine Spell cards. Doing so, Chazz, Alexis, Atticus, and Hassleberry got sacrificed. Syrus was the only one to survive. Doing so Jaden was in rage and started to become the Supreme King. After Brron was defeated, he mentioned that he was just a pawn and that Yubel was the true being responsible for everything that's happened. He also mention that Jesse, Jaden's friend, was with the stars, not before Brron disappeared as well.
Brron's deck is a Dark World Deck. His strongest monster that was summoned was Reign-Beaux, Overlord of Dark World, however Brron mention he has a monster that was practically unstoppable called; Colorless, Chaos King of Dark World. But Brron never got the chance to summon his monster since he was defeated.