Zexion, the Cloaked Schemer, is the Nobody of Ienzo and is Rank VI in Organization XIII and an antagonist in Riku's storyline in Kingdom Hearts: Chain of Memories. He weaves illusions to fight for him. Unlike the other Organization members, Zexion's weapon was originally unknown, and his talents were used only outside of normal combat. In Kingdom Hearts Re:Chain of Memories, Zexion's weapon was revealed to be a book called a Lexicon.
Source from Wikipeida