Zexion is a manipulator appearing in Chain of Memories. He is also known as the “Cloaked Schemer.” Zexion’s original self was Ansem the Wise’s youngest lab assistant, and named Ienzo. He convinced Ansem the Wise that they should build an underground lab for research. He is voiced by Akira Ishida and Vincent Corazza in the Japanese and English versions of Kingdom Hearts Re:Chain of Memories, respectively. Zexion uses his power of illusion used to mimic others’ weapons, disguise himself as others, and create duplicates of himself, and wields a lexicon as his unique weapon. Before Kingdom Hearts II Final Mix, Zexion’s weapon and powers were unknown because he had died without fighting. Because Nomura was unsure if it would be revealed later, he kept information about it secret. The development team also destroyed his gravestone in the World That Never Was that would have shown his weapon.

Zexion is one of two Organization members who appear only in Riku’s story in Chain of Memories. Originally, Zexion had planned to use Riku against Marluxia and his co-conspirators. But as Sora dealt with them, Zexion sees Riku to be of no use and personally attempts to destroy him in his own way. Drawing Riku into a simulation of Destiny Islands, Riku’s homeworld, Zexion tells Riku about how he is to blame for the islands being destroyed. He then assumes the guise of Sora and attacks Riku, telling him that he’s become a pawn of the darkness. He engulfs Riku in light, but Naminé’s intervention in Kairi’s form convinces Riku to accept darkness and light. With newfound confidence, Riku follows Zexion’s scent through the light and causes Zexion to flee. Afterwards, Axel brings the Riku Replica to Zexion and convinces the replica that he can become “real” by gaining power that the real Riku does not have. The replica agrees, and as per Axel’s suggestion, kills Zexion.
From Wikipedia