Short answers, pulled from the story.
Big Boss is a major character in Konami's Metal Gear action-adventure stealth game series, created by Hideo Kojima. He serves as both protagonist and antagonist across the franchise, appearing first as Solid Snake's commanding officer in the original Metal Gear (1987) before being revealed as the secret leader of Outer Heaven.
Les Enfants Terribles was a covert government cloning program that used Big Boss's DNA to produce three genetically altered sons: Solid Snake, Liquid Snake, and Solidus Snake. Big Boss ultimately leaves Zero's organization after learning his DNA was used without his consent for the project.
Big Boss is voiced by Akio Otsuka in Japanese and David Hayter in English for most of the series. Kiefer Sutherland replaced Hayter in Metal Gear Solid V: The Phantom Pain, following a suggestion to Hideo Kojima from Hollywood producer and director Avi Arad. The elderly Big Boss in Metal Gear Solid 4 is voiced by Chikao Otsuka, Akio Otsuka's real-life father, in Japanese.
Venom Snake is a body double for Big Boss, originally a physician and medic in MSF. After the destruction of Mother Base, he was placed in a coma and subjected to facial reconstruction and brainwashing by Cipher to impersonate Big Boss. He serves as the true protagonist of Metal Gear Solid V: The Phantom Pain and is later retconned as the Outer Heaven leader killed by Solid Snake in the original Metal Gear.
Artist Yoji Shinkawa designed Naked Snake at Hideo Kojima's request, making him visually similar to Solid Snake but conveying a younger, more naive personality. An earlier version of Big Boss in Metal Gear 2: Solid Snake had been visually inspired by actor Sean Connery before Shinkawa's design replaced it.
Big Boss and Major Zero disagreed over how to honor their mentor The Boss's final wish for a world where soldiers fight freely. Zero used that vision to justify imposing order and control, while Big Boss rejected that interpretation. Big Boss further left after discovering his DNA had been used for the Les Enfants Terribles cloning project without his knowledge, and later staged the coups represented by Outer Heaven and Zanzibar Land against Zero's organization.