Metal Gear Solid is direct son of Metal Gear and Metal Gear 2 - Solid Snake, both made at the end of 80s. This new episode was reconsidered by Konami at the beginning of 2000, with a first release on Playstation and later ported to PC and other systems. According to several sources MGS is the inventor of a genre, the stealth games since its first version, although the 3D story produced with Metal Gear Solid gave the commercial success it deserves. Despite of many action games here you will have not to kill your enemies (well, finally you will kill someone) but hide yourself in a spy-story environment.
Here it is what Wikipedia says about this kind of games:
"Stealth games in the genre typically allow the player to remain undetected by hiding, using disguises, and/or avoiding noise. Some games allow the player to choose between a stealthy approach or directly attacking antagonists, perhaps rewarding the player for greater levels of stealth. The genre has employed espionage, counter-terrorism and rogue themes, with such protagonists as special forces operatives, spies, thieves, assassins and ninjas. Some games have combined stealth game elements with those of other genres, such as first-person shooters or platform games."