Organization XIII and uses the ice element and a shield-like weapon to fight. He first appears in Kingdom Hearts: Chain Of Memories. His nickname "The Chilly Academic" personified his specialty with science and experimentation. As a results of his experiments, he managed to create a replica of Riku who was made to believe that he was the real Riku. It was part of the plan to manipulate Sora for the Organization. After Sora defeated Vexen in Twilight Town, Vexen almost revealed the truth about his other half, but Axel terminated him before he could say that.
In his previous life, Vexen was Even, yet another of Ansems scientists. You see some of him in Kingdom Hearts: Birth by Sleep as Even, and Aqua, Ven, and Terra are apparently aqquainted with him,
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