Metal Gear is a series of video games created by Hideo Kojima and developed by Konami. In the games, the player usually takes control of Solid Snake, a special forces operative, in a bid to destroy various incarnations of a bipedal tank (a Metal Gear), although the individuals in control of the Metal Gear and their motives are usually somewhat different from game to game. The main focus of game play is on sneaking and defeating enemies through stealth rather than brute force, offering a wide variety of different ways to avoid or get the drop on enemy sentries (most infamously, a cardboard box). As the series progresses, things tend to mess with the minds of the characters and the player to greater and greater extents.
This does not stop them being rather good.