The character of Solid Snake is based on Snake Plissken, Kurt Russell's character in 1997: fuga da New York (1981) (which is reportedly one of Hideo Kojima's favorite movies).
The character on the cartridge that is supposed to be Solid Snake is actually Kyle Reese (played by Michael Biehn) from Terminator (1984)
Hideo Kojima came up with the stealth-based gameplay with the MSX2's hardware limitations in mind. Since the MSX could barely handle conventional action games (due to the fact that the screen would flicker when too many animated objects were present, and the hardware couldn't handle scrolling very well), Kojima decided to make a game where the player had to avoid contact with the enemy instead of fighting. Kojima got the idea from La grande fuga (1963) and originally wanted to make the game about a POW escaping from the enemy's prison. However, Kojima's co-workers advised him that a game based solely on avoiding the enemy wouldn't work by itself and that the player would need to have something to defend themselves with whenever the player is discovered. As a result, the original escape premise was replaced by an infiltration premise. Kojima took the infiltration premise from I cannoni di Navarone (1961).
The codename of Snake's mission (Operation: Intrude N313) is actually an inside joke regarding the development of the game. After Hideo Kojima's earlier game, "Lost Warld," was cancelled, he was assigned to work on a nearly cancelled military-themed game bearing the working title of "Project N312." Kojima departed from the game's original premise and gradually turned the game into what eventually became Metal Gear. In the game, Grey Fox's failed mission was titled "Operation: Intrude N312."
The whole Metal Gear series has sold over 14 million units worldwide to the start of 2004.