Vexen

Vexen (ヴィクセン, Vikusen) is a Nobody known as the "Chilly Academic" (いてつく学究, Itetsuku Gakkyū). Vexen's original self is a scientist named Even (エヴェン), whose interest in studying Xehanort's memories results in him becoming a Nobody. Vexen can control ice and carries a large shield called Frozen Pride (フリーズプライド, Furīzu Puraido, lit. "Freeze Pride") in battle. The character first appeared in Kingdom Hearts: Chain of Memories, where Tatsuya Kando provided the voice for simple battle expressions. Vexen was included as an optional boss in the Japanese exclusive Kingdom Hearts II Final Mix, and was voiced by the late Nachi Nozawa. Nozawa also provided voice acting for dialogue in Kingdom Hearts Re:Chain of Memories and Kingdom Hearts: 358/2 Days. Vexen's English voice acting was done by Derek Stephen Prince.
As revealed in 358/2 Days, Vexen experiments with the creation of Replicas, the first of which is Xion. In Chain of Memories, Vexen occupies the basement of Castle Oblivion with Lexaeus and Zexion, who he sides with to prevent Marluxia's plan to overthrow the Organization, later being assigned to personally investigate Marluxia's intentions. He battles Riku in order to gather data to create a Replica of him, and allows Naminé to manipulate the Replica's memories to test Sora's worth. After the Replica fails to defeat Sora and Marluxia threatens to reveal the shortcoming to Xemnas, Vexen fights Sora himself and gives him a card to access Twilight Town in Castle Oblivion with the intention of revealing to Sora both Roxas' existence and Marluxia's plan. As a result, Marluxia declares Vexen a traitor and sends Axel to eliminate him, which Axel does by incinerating Vexen before he can reveal the truth to Sora, mainly to gain Marluxia's trust and prevent him from using Vexen's Replica research. Vexen's death, coupled with that of his unseen Heartless, leads to the restoration of Even as seen in Kingdom Hearts 3D: Dream Drop Distance.