Ocelot
06
After pushing FOXHOUND to action in the 2005 Shadow Moses Incident, Ocelot united with the private forces of Russian colonel Sergei Gurlukovich and passed along the plan to restore the Soviet Union to Liquid Snake.
Even then, however, his actions were part of an elaborate ruse.
He was acting on behalf of President George Sears (Solidus Snake). His goal as Solidus's spy was to acquire the test data from the latest Metal Gear and prototype nuclear warhead and submit it to President Sears, then watch the conflict between Solidus and Liquid Snake unfold.