Vexen is a scientist who appears in Kingdom Hearts: Chain of Memories. He is also known as the "Chilly Academic". Vexen's original self was Even, and he was interested in studying Xehanort's memories. Vexen can control ice and carries a large shield in battle that blocks any frontal attacks made against him. Vexen is voiced by Tatsuya Kando in Kingdom Hearts: Chain of Memories and Nachi Nozawa and Derek Stephen Prince in Kingdom Hearts Re:Chain of Memories.

In Chain of Memories, Vexen sides with Zexion and Lexaeus, other members occupying the castle's basements, to prevent Marluxia's plan to overthrow the Organization. He first battles Riku in order to gather data to create a replica of him. However, Vexen cares nothing for his "experiment" and allows Naminé to manipulate the Riku Replica's memories against his wishes. When the Replica fails to defeat Sora, Marluxia threatens to reveal the shortcoming to Xemnas, forcing Vexen to kill Sora. Encountering Sora, Vexen says that he came to collect his "debt" and provokes Sora's anger by making him believe that he controlled Riku rather than created a replica.

After their battle, Vexen gives Sora the card to Twilight Town with the intention of revealing Roxas's existence. Marluxia considers him a traitor as a result and sends Axel to kill him. In Twilight Town, Vexen attempts to reveal to Sora why he feels as though he has been to Twilight Town despite being fairly certain that he had never been there. Sora and Vexen battle again after Vexen tells Sora to throw away his memories and listen to his heart. As Vexen is about to reveal Marluxia's plot, he is killed by Axel.