vexen

Vexen approaches problems like an intellectual, with a hypothesis and a method to test those hypotheses. He appears to view life as a grand experiment. 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 reminds 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 behaviour. Although not explicit, given his attitude, he may not understand why Saïx, a member three ranks lower, is technically second-in-command and not Xigbar.
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 Room of Sleep, and took Zexion's suggestion to approach Xemnas there as a joke.
Ironically, Vexen's throne is the lowest of the Organization in their meeting chamber known as Where Nothing Gathers. This is mostly due to his recurring incompetence and preference of not sullying his hands like Zexion, though the latter can easily hold his own in battle. This also reinforces the trait of cowardice in Vexen, displayed through his fear of Xemnas and his fear of death.
In the Chain of Memories manga, Vexen appears as a character who thinks that he doesn't get enough respect from the aboveground members. He is also met by Sora, Donald, and Goofy right after they confront the Riku Replica for the first time, while in the original game, they fought the Riku Replica twice before fighting Vexen two floors later.