The original Metal Gear, released in 1987 for the MSX2 home computer, is the start of what would many years later become a huge franchise spanning decades of work and extensive amounts of lore. This is our first introduction to both Solid Snake and Big Boss, two characters who would later become the main faces of the franchise.
Despite it's limited and simple dialogue, it's clear to see the beginning of themes that would continue throughout the series. The ones that stand out to me in particular are those of betrayal, with the reveal that Big Boss, who had been giving Snake commands throughout the game, was actually the leader of Outer Heaven.