Big Boss is the main antagonist of the NES version of Metal Gear and Snake's Revenge. He serves as the main antagonist, last boss of the first game, penultimate of the second and is the central enemy of Solid Snake. While he vaguely resembles his original counterpart, this version of him is much worse, lacking any of the redeeming qualities of the former.
He sends Snake into the jungle and instructs him to infiltrate Outer Heaven and destroy Metal Gear.
When Snake stops the threat of Metal Gear, he is intercepted by Big Boss who enters a gun fight with Snake to try an prevent his escape.
In Snake's Revenge, Big Boss got a mechanical body and built another base. During this time, Big Boss also built another Metal Gear and put nuclear weapons on it to launch at several major locations, including Washington, Paris, and Tokyo.
At the end of Metal Gear: Snake's Revenge, Big Boss is revealed to have a brand new mechanical body and challenges Snake to fight him. After a few hits, Big Boss transformed his mechanical pieces into a gargantuan metal figure, which he gloated that had no weak points, however, this is shown to be false as Snake put mines below him to blow his mecha body and killing him for real.