This is part of a sub-series tributing the members of Organization XIII, the villianous organization present in Kingdom Hearts II, Chain of Memories, and 358/2 Days.
Vexen, no. IV, is "The Chilly Academic." He is the Nobody of Even. He is the developer of the replicas used by the Organization, and uses ice and shields during combat. He appears in Chain of Memories and briefly in 358/2 Days.