Big Boss was the codename of the legendary soldier who founded the U.S. Army Special Forces Unit, FOXHOUND. He was also the founder and commander of Militaires Sans Frontières, the "soldiers without borders," which led to the creation of Outer Heaven in South Africa. Big Boss later helped the small nation of Zanzibar Land achieve independence in Central Asia, becoming its head of state. Big Boss was considered by many to be "The Greatest Warrior of the 20th Century" and a brilliant military leader and was hailed as a war hero by admirers and feared as a tyrant by his enemies. As a result of the Les Enfants Terribles project, he was the genetic father of Solid Snake (his subordinate and later nemesis), Liquid Snake and Solidus Snake.

Prior to earning the codename of Big Boss, he served as a field operative for the CIA black ops unit FOX (Force Operation X) which was founded by Zero and the apprentice of The Boss under the codename of Naked Snake during the Cold War.