The Metal Gear franchise, created by Hideo Kojima and featuring character and mecha designs by Yoji Shinkawa, features a large cast of characters, several of whom are soldiers with supernatural powers provided by scientific advancements.

The series initially follows the mercenary Solid Snake. In the Metal Gear games, he goes on government missions to find the Metal Gears while encountering Gray Fox and Big Boss in Outer Heaven and Zanzibar Land. In the Metal Gear Solid games, he works with Otacon and Raiden while opposing Liquid Snake's FOXHOUND, Solidus Snake, the Patriots and Revolver Ocelot. Beginning with Metal Gear Solid 3: Snake Eater, several games have served as prequels, following Big Boss' past as Naked Snake and Venom Snake as well as the origins of the organizations.

While the characters of the Metal Gear games had designs modeled after Hollywood actors, the Metal Gear Solid games established consistent designs based on Shinkawa's idea of what would appeal to gamers, with several characters that he designed following ideas from Kojima and staff. Critical reception of the game's cast has been positive, with publications praising their personalities and roles within the series.

Metal Gear began as a pastiche of action films of the time and its characters were pastiches of contemporary action movie heroes. When Shinkawa began designing the characters for PlayStation's Metal Gear Solid, they were given their respective established visual appearances. Due to hardware limitations, Shinkawa designed them to appeal to gamers. Because of the time skip between titles, some characters were redesigned to fit in the game's setting. With the improved technology of consoles like the PlayStation and PlayStation 2, starting with Metal Gear Solid 2: Sons of Liberty the staff gave the characters a more realistic look, despite their initial doubts. This caused difficulties for the staff, as they had to make the faces more realistic. When illustrating characters, Shinkawa does not focus on minor details such as eyes, instead illustrating something more symbolic. While Solid Snake was easy to illustrate due to having a consistent design, with Big Boss's younger self, Naked Snake, being conceived via minor changes to his original version, other characters' designs were more time-consuming.

When they debuted, player characters Solid Snake and Raiden were meant to represent the player, though in subsequent games they gained more defined personalities. As Snake became more experienced in combat throughout the series, Kojima attempted to create more challenging antagonists for boss fights. This resulted in Big Boss's clones from Metal Gear Solid and Metal Gear Solid 2, who have the same abilities as Solid Snake, the Cobra Unit from Metal Gear Solid 3: Snake Eater, who participated in World War II, and the Beauty and the Beast Corps from Metal Gear Solid 4: Guns of the Patriots, who possessed few human traits. While the villains in the first games had detailed backstories, the Cobra Unit members were intended to have little information known about them, resulting in a significant impact among players upon their deaths. This also made it difficult for Shinkawa to conceptualize their visual appearance, as he had little to no background information. By Metal Gear Solid 2, Kojima was inspired by the Sherlock Holmes novels to introduce a sidekick character in order to view Snake from a different perspective.

Metal Gear Solid marked the first time that characters had voice actors, with Solid Snake and Naked Snake being voiced by Akio Ōtsuka in Japanese. Ōtsuka remembers being surprised during his debut as a result of the large amount of dialogue Snake was given. In English, casting was directed by Kris Zimmerman and supervised by a member of Konami. Solid Snake's English voice actor was David Hayter, who, despite having issues with some of the dialogue in Metal Gear Solid, became attached to the series.

Various Metal Gear Solid games have been expanded upon in remakes and other media, such as Metal Gear Solid: The Twin Snakes, Metal Gear Solid: Digital Graphic Novel, Metal Gear Solid 2: Digital Graphic Novel, and Metal Gear Online.

Solid Snake (ソリッド・スネーク, Soriddo Sunēku), real name David (デイビッド, Deibiddo) and otherwise known as Iroquois Pliskin (イロコィ・プリスキン, Irokoi Purisukin) and Old Snake (オールド・スネーク, Ōrudo Sunēku), is the main protagonist of the original series. In the original Metal Gear games, he is a rookie FOXHOUND agent tasked with finding and destroying the Metal Gears in Outer Heaven and Zanzibar Land, leading to confrontations with his comrade Gray Fox and superior Big Boss (the phantom in Outer Heaven and his father in Zanzibar Land). Snake befriends Otacon while fighting the corrupt FOXHOUND, led by his terrorist twin brother Liquid Snake in Metal Gear Solid, and assists Raiden in fighting Solidus Snake and the Patriots in Metal Gear Solid 2: Sons of Liberty. In Metal Gear Solid 4: Guns of the Patriots, he returns as protagonist, with an accelerated aging process. Solid Snake is voiced by Akio Ōtsuka in Japanese and by David Hayter in English.