Board Thread:Questions and Answers/@comment-74.80.21.175-20150215013110/@comment-24745807-20150216143740

Ocelot lost his arm in MGS. Sometime between the Shadow Moses Incident and the Tanker Chapter in MGS 2, Ocelot had Liquid's arm grafted onto his body. Throughout MGS2, Ocelot's body was "taken over" by Liquid through his arm (not sure if specifics were explained). Finally, at the end of MGS2, Liquid took control of Ocelot completely, so in MGS4, Liquid is the bad guy. He's just using Ocelot's body as a vessel. Really, I guess Ocelot and Liquid wanted to achieve the same things as Big Boss; freedom from the control of the Patriots, but it is Liquid's mind in Ocelot's body.