Cyborg Ninja

Someone else has also infiltrated the Nuclear storage facility other than Solid Snake. And that someone is this mysterious Cyborg Ninja. He is first scene when he saves Baker and cuts off Rovolver Ocelot's hand.

Spoiler: The Cyborg Ninja is actually Gray Fox, the asumed dead elite member of Fox hound. He did die, but he was taken to a lab and revived by Dr. Clark. He was fitted with the exoskeleton and they experimented on him. Eventually he escaped when a lab accident occured and was pressumed dead. He is seaking death. And at one point he acted as the big brother of Naomi after he killed her parents on a mission. He felt guilty about it and couldn't kill her or tell her.