The Metal Gear series is a complicated, circular mess of plotlines filled with surprises, twists, and betrayals. It's a mess we love, but it's still a mess. Even if you've been paying attention, you may have missed some things. If you've been away from the series for a while, or are maybe approaching it for the first time, some catch-up isn't a bad idea.
Warning: This article will contain heavy spoilers for games in the Metal Gear series released prior to Metal Gear Solid V: The Phantom Pain.
If I missed any major characters or got any plot points wrong – I fact-checked this as best I could, but this is Metal Gear we're talking about here – jump into the comments to add in your two cents.
Solid Snake is the protagonist of Metal Gear, Metal Gear 2: Solid Snake, Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty, and Metal Gear Solid 4: Guns of the Patriots.
To gamers, Solid Snake is the original Snake, appearing in the very first Metal Gear and again in its revival, Metal Gear Solid. Snake is a clone of Big Boss, the product of an experiment to clone the ultimate soldier. Throughout his career he would take down multiple Metal Gears, learning about the legacy of a secret society called The Patriots.
Snake would end up taking down the Patriots even as his cloned body aged rapidly.
Naked/Venom/Punished Snake/Big Boss
The original Snake appears in Metal Gear Solid 3: Snake Eater, Metal Gear Solid: Portable Ops, Metal Gear Solid: Peace Walker, Metal Gear Solid V: Ground Zeroes and Metal Gear Solid V: The Phantom Pain before appearing as the villain in Metal Gear and Metal Gear 2: Solid Snake, with a cameo in Metal Gear Solid 4: Guns of the Patriots.
Naked Snake, however, is the original Snake: Big Boss. First appearing in Metal Gear Solid 3: Snake Eater, Snake's first big mission is to eliminate the woman who trained him, The Boss, and destroy the progenitor to the Metal Gear walking tank, the Shagohod. Snake loses one of his eyes during torture, getting his trademark eye patch, as well as meeting Revolver Ocelot for the first time.
Liquid appears in Metal Gear Solid and Metal Gear Solid 2: Sons of Liberty. He, like Solid Snake, is an imperfect clone of Big Boss. After Roy Cambell and Solid Snake left FOXHOUND, Liquid Snake took control and turned the squad into a terrorist unit that took over Shadow Moses Island. Liquid would die during a fight with Solid Snake, only to return – in a way – when Revolver Ocelot took his arm to replace his own newly missing one.
Solidus Snake appears primarily in Metal Gear Solid 2: Sons of Liberty. In the Metal Gear timeline, Solidus Snake, going by the name George Sears, became President of the United States, but was removed by The Patriots as part of covering up the incidents on Shadow Moses Island in Metal Gear Solid. Solidus would go on to orchestrate the events of Metal Gear Solid 2: Sons of Liberty, posing as Solid Snake, only to be stopped by Raiden, his adopted son.
Revolver Ocelot (ADAM/Shalashaska/Liquid Ocelot)
Aside from Big Boss, Ocelot might be the character to appear in the most Metal Gear Solid titles.
His first appearance in the series (in release order) is Metal Gear Solid, where he's remembered fondly by fans for classy lines like "I love reloading during a battle! There's nothing like slamming a long silver bullet into a well-greased chamber," just after bragging about his Colt Single Action Army revolver moments before.
Snake's first encounter with Ocelot would end with the revolver wielding cowboy losing his hand to the Cyborg Ninja's blade, though he would end up replacing it with that of his fallen comrade, Liquid Snake, as he went on to appear in the other Metal Gear Solid titles.
His first appearance in the story, however, occurred in Metal Gear Solid 3: Snake Eater, where Naked Snake encountered him in battle and defeated him before suggesting that he switch to revolvers instead of the more modern semi-automatic pistol he was using. Ocelot would be nearly as big a behind the scenes player as Zero, joining Naked Snake in The Patriots, with whom he'd continue to work as a spy before eventually attempting a takeover of his own in Metal Gear Solid 4: Guns of the Patriots.
Master Kazuhira Miller (Master McDonnell Miller)
Kazuhira Miller appeared in Metal Gear Solid originally, but he had actually been killed and then impersonated by Liquid Snake. He finally appeared in person in Metal Gear Solid: Peace Walker, but was a codec face before that in Metal Gear 2. He was instrumental in the formation of Big Boss' Militaires Sans Frontieres group, and plays a major role in Metal Gear Solid V: The Phantom Pain.
Gray Fox (Frank Jaeger/Null/Cyborg Ninja)
Gray Fox, real name Frank Jaeger, first appeared in the original Metal Gear when Solid Snake was tasked with rescuing him from Outer Heaven. In Metal Gear 2: Solid Snake, Snake would end up fighting Jaeger, who had reallied himself with Big Boss.
Before that, though, Jaeger was a child soldier who would be experimented on as a teenager in Metal Gear Solid: Portable Ops, being called Null in that game and battling Big Boss.
Grey Fox's final and probably most famous appearance, though, is as the Cyborg Ninja in Metal Gear Solid. After dying in Metal Gear 2: Solid Snake, Jaeger was once again experimented on, this time being remade as a cyborg ninja, complete with optic camouflage and katana. Jaeger came after Solid Snake, single-mindedly bent on battling him. When Snake defeated him, the ninja disappeared, only to come to his senses – and Snake's aid – one last time during Snake's final battle with Liquid before being crushed by Metal Gear REX.
The Big Boss Era
The woman called The Boss trained Naked Snake in the ways of war before betraying her country in Metal Gear Solid 3: Snake Eater. It would turn out, though, that the betrayal was also a cover. Eventually, Naked Snake would have to kill her and take her place to avert nuclear war.
Zero (Major Zero, Major Tom, Cipher)
Major Zero acted as one of Snake's primary guides in Metal Gear Solid 3: Snake Eater, but would go on in behind-the-scenes parts of the series to form The Patriots, initiate the Les Enfants Terribles project, which created Solid, Liquid, and Solidus Snake. His control of The Patriots and other organizations throughout the Metal Gear series makes him one of the primary antagonists despite very few appearances.
Paz was one of the main characters of Metal Gear Solid: Peace Walker, a spy for Cipher/Zero and The Patriots. She attempted to launch a plan to launch nukes toward the United States and frame Big Boss' Militaires Sans Frontieres organization, but that ultimately failed. She was thought dead but reappeared in Metal Gear Solid V: Ground Zeroes, having been captured and brutally interrogated before being implanted with bombs and used as an unwilling human decoy to attack Big Boss at the end of that story.
Chico is a child soldier rescued by Big Boss during Metal Gear Solid: Peace Walker. He joined Militaires Sans Frontieres and prior to Metal Gear Solid V: Ground Zeroes was captured by Skull Face in an attempt to rescue Paz. Like Paz, he was brutally interrogated before being rescued by Big Boss, only to die in the explosion resulting from the bombs implanted in Paz.
Skull Face is the main antagonist of Metal Gear Solid V: Ground Zeroes and The Phantom Pain. He was gravely injured and tortured growing up, giving him horrific scars, but he eventually went on to command the XOF and Parasite military units. In Ground Zeroes, he tortures Paz and Chico to get to Big Boss and Cipher, the latter of whom he infected with the parasite that left him invalid as seen at the end of Metal Gear Solid 4: Guns of the Patriots.
The Solid Snake Era
Roy Campbell, who first appeared in Metal Gear 2: Solid Snake, and again in Metal Gear Solid and Metal Gear Solid 2: Sons of Liberty in addition to making some cameos in other games in the series, is pretty much a straight lift of Colonel Trautman from the Rambo films. Snake is a bandanna wearing, war-weary soldier, and Campbell is his stoic, fatherly handler, just as with John Rambo and Colonel Trautman.
Hal "Otacon" Emmerich
Hal "Otacon" Emmerich was introduced in Metal Gear Solid as the designer of Metal Gear REX. Once he realized how his creation would be used, he regretted it and began assisting Solid Snake.
Otacon would serve through his appearances in Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty, and Metal Gear Solid 4: Guns of the Patriots, as Solid Snake's tech team, supplying him with information, hacking anything that needed hacking, and inventing tech for Snake.
Otacon also acts as a sort of self-insert for Kojima and the player – the dorky anime fan, wetting his pants in the face of fear, using his tech skills to do good.
Raiden is perhaps the most hated character in the series' long history. Raiden appeared first in Metal Gear Solid 2: Sons of Liberty in one of the biggest bait-and-switch moves in gaming. With gamers expecting to play as hero Solid Snake, they were surprised when, just a few hours into the game, they took control of the skinny, white-haired character and never had the option to switch back.
Kojima was interested in developing Snake from a third person perspective and wanted to give players someone younger to play as. Fan response was extremely negative in America. It's possible, if it had been positive, that Raiden could've taken over the role of the series protagonist and we could've gotten a more linear series, or at least one that branches.
In the context of Metal Gear Solid 2: Sons of Liberty, Raiden was the agent tasked with infiltrating the Big Shell off-shore structure to rescue the President of the United States along with other hostages taken by the Dead Cell terrorist group lead, supposedly, by Solid Snake. It's eventually revealed that another of Big Boss' clones, Solidus Snake, is Raiden's father
Raiden got a second chance to make an impression on fans when he appeared in Metal Gear Solid 4: Guns of the Patriots as a new version of the Cyborg Ninja. As Kojima expected, fans received this grizzled, superhuman version of the character much more warmly, especially in light of him not being a playable character, though he would get his own chance to shine in Metal Gear Rising: Revengeance, an action game developed by Platinum Games.