Metal Gear is an action-adventure stealth video game developed and published by Konami for the MSX2. It was released for the system in Japan and parts of Europe in 1987. Considered the game to popularize the stealth game genre, it was the first video game to be fully developed by Hideo Kojima, who would go on to direct most of the games in the Metal Gear series. A reworked port of the game was released for the Famicom a few months later, which later saw release in international markets for the NES over the following two years; this version was developed without Kojima's involvement and features drastically altered level designs, among other changes. An emulated Famicom version came with the special edition of Metal Gear Solid: The Twin Snakes on GameCube. A more faithful port of the MSX2 version was later included in Metal Gear Solid 3: Subsistence for the PlayStation 2, as well as in the HD Edition of the same game released for the PlayStation 3, Xbox 360 and PlayStation Vita, with these newer ports featuring a revised translation and additional gameplay features. The MSX version was also released for Wii Virtual Console and PC.

A stealth game is a type of video game in which the player primarily uses stealth to avoid or overcome opponents. Games in the genre typically allow the player to remain undetected by hiding, sneaking, or using disguises. Some games allow the player to choose between a stealthy approach or directly attacking antagonists, but rewarding the player for greater use of stealth. The genre has employed espionage, counter-terrorism, and rogue themes, with protagonists that are special forces operatives, special agents, secret agents, thieves, ninjas, or assassins. Some games have also combined stealth elements with other genres, such as first-person shooters and also platformers.