5. He may not show his true colors when Sora first meets him in Castle Oblivion, but this double agent is not all that he appears to be. In fact, he would do anything to save his friend, no matter who he would have to go through. Who is it?
From Quiz The Characters of "Kingdom Hearts"
Answer:
Axel
In "Kingdom Hearts: Chain of Memories", Axel pretends to be on Marluxia and Larxene's side as he confronts Sora and even destroys one of his own, Vexen, on Marluxia's orders. In the end, he sets Marluxia's defeat into motion by releasing the young witch, Namine. In "Kingdom Hearts 2", he travels to the virtual Twilight Town to take his friend, Roxas, back from the scheming hands of DiZ. Riku Replica, although determined to rescue his supposed friend Namine, was not a double agent.