Vexen

Vexen approaches problems like an intellectual, with a hypothesis and a method to test those hypotheses. He is haughty, erudite, proud and stubborn, 36 years old and 6'4" tall. He appears to view life as a grand experiment, suiting his title as "The Chilly Academic". He appears very much like the stereotypical 'mad scientist'. More than any other member, save Xemnas, he considers his numerical rank a literal one and will often deride members with lower numerical rankings than his; he reminded Marluxia of his superior rank when Marluxia orders him not to "disappoint us" again and addresses Zexion by his inferior rank when Zexion lamented Vexen's impatience, but is often chastised by others for this behavior.

Interestingly, 358/2 Days shows a more understanding side to Vexen's character; he is seen patiently guiding Roxas in the aspects of reconnaissance and gave the latter all the time he wanted to examine the town even more, before finally ending the mission with valuable advice. However, Vexen was irritated by Roxas only being able to "look, but not see"; in other words, making sense of the data he was gathering. He felt proud of himself when it looked like his teaching was paying off with Roxas - "small steps for small minds."

Vexen also displays a fear of Xemnas, immediately bowing to Marluxia's demand to destroy Sora when Marluxia threatened to tell Xemnas of the failure of the Riku replica. He also feared to approach Xemnas while the latter was in the Chamber of Repose, and took Zexion's suggestion to approach Xemnas there as a joke.

In the Kingdom Hearts: Chain of Memories manga, Vexen appears as a character who thinks that he doesn't get enough respect from the upper floor members.

After reacquiring his humanity, Vexen, now having the heart to feel horror and shame for what he did, became determined to atone for his sins and only re-joined the Organization in order to help ensure its defeat. Although acting still as a passionate scientist, in truth Vexen was more than willing to risk his life to atone, which Demyx couldn't help but call him out for, and he uses his intelligence to successfully coax Demyx into joining him.

Vexen wears the basic Organization uniform of a black coat with like-colored boots and gloves, though the sleeves of Vexen's cloak are a bit longer than normal and partially cover his hands. His cloak is also the longest out of all the members having it almost like a gown that covers his boots. Vexen sports dirty blond hair (which was a somewhat brighter shade of yellow in the Gameboy version of Chain of Memories), worn long with two slightly shorter (but still long) bangs that frame his face. He also has rather large, bright green eyes.