Metal Gear is a series of stealth video games, the first game of which was released in 1987 for the MSX2. Metal Gear 2: Solid Snake (Metal Gear Solid outside Japan), the second game of the Metal Gear series, was released in 1990 for the same platform. Metal Gear is one of Hideo Kojima’s most famous works and it inspired a lot of sequels and spin-offs. Metal Gear 2: Solid Snake – Night Fall is the only full Metal Gear 2 OST that was ever released, as far as I know(?).
The original Metal Gear is said to be inspired by movies such as Escape from New York, Metalstorm and Mad Max. In Metal Gear Solid V, Metal Gear’s history is retconned so that Metal Gear 2: Solid Snake – Night Fall is said to take place during the events of Metal Gear.
The canonicity of Metal Gear 1 and Metal Gear 2: Solid Snake – Night Fall are contested because Metal Gear 1 was meant to be a script for an unmade movie and Metal Gear 2: Solid Snake – Night Fall was never meant to be part of the Metal Gear canon. Metal Gear 1 and Metal Gear 2: Solid Snake – Night Fall have many differences from Metal Gear 3 onward, so Metal Gear’s official history begins with Metal Gear 3 on the MSX2 console.