Liquid Snake is a genetic clone of the world's greatest soldier, Big Boss. In an effort to recreate Big Boss, the Les Enfantes Terrible project was started by the Patriots and run by Dr. Clark, the Patriot known as Para-Medic. Two clones were created as Solid Snake is Liquid's twin brother. Liquid was born in 1972 to surrogate mother and Patriot, code name, EVA. Liquid gained all of Big Boss's superior genes even though he had been told otherwise. The Les Enfantes Terrible project is the push factor for Big Boss to have left The Patriots.
Raised to be a perfect soldier, Liquid grew up in the UK and joined the British SAS (where he got his accent). He fought in the first Gulf War, where he was tasked by the British Secret Intelligence Service (SIS) to infiltrate the Middle East as a sleeper agent. However he was captured by the Iraqis before he could complete his mission. He was eventually rescued by the US in 1994. Liquid joined FOXHOUND in 2000 in which he became the field commander, after Solid Snake and Colonel Roy Campbell had already retired from FOXHOUND. Some time before 2005, Liquid became aware of his heritage and believed he was the flawed clone of Big Boss; he was probably informed by President and Big Boss' perfect clone Solidus Snake. At this point Liquid started to harbour an immense hatred of his "brother" Solid Snake, both for being the "superior" clone of Big Boss and for having denied him a chance at revenge against their father (after Snake killed him in Zanzibar Land), the man Liquid believed chose him to be the "imperfect clone." Liquid started the FOXHOUND uprising at Shadow Moses in 2005. Liquid named his rebel group "The Sons of Big Boss".
As a result of his belief that he was the "inferior" clone, Liquid held a strong resentment towards Solid Snake, who supposedly inherited the better genetics, and wished to defeat him in combat and reclaim what he felt was his birthright, thus proving his superiority.
Liquid was 182 cm tall, had an IQ of 180, and spoke seven languages fluently. He was almost an exact double of Solid Snake in terms of appearance, with the only distinguishable feature being his darker skin tone and hairstyle (though it should be noted that Solid Snake, when he was "summoned" from Alaska, originally had the same hairstyle as Liquid, but he cut his hair just prior to being sent to Shadow Moses Island so that he "won't be mistaken for Liquid."). He also had a tattoo on his left arm, which resembled the Rod of Asclepius, but with a sword in its place.
Liquid Snake (voiced by Cam Clarke and Banjo Ginga) serves as Metal Gear Solid's main antagonist against Solid Snake. Liquid leads FOXHOUND, Solid Snakes old unit, and the Genome Soldiers, to capture a nuclear waste disposal facility of Shadow Moses Island. He demands that the remains of Big Boss be handed over to him, threatening to launch a nuclear missile if ignored. Before the events of the game, Liquid murders Snake's former survival coach Master McDonnell Miller and assumes his identity. He tricks Snake into activating the new version of Metal Gear, Metal Gear REX. Solid Snake is then forced to fight Liquid in a series of battles, first with Liquid piloting Metal Gear REX, secondly in a bare handed fist fight, and finally in a car chase. Although defeated three times, Liquid still manages to get the upper hand and dies due to the FOXDIE virus just before killing Solid Snake. Dr. Naomi Hunter coded the FOXDIE virus specifically to target the dominant genes of Big Boss, which she believed would kill Solid Snake, but killed Liquid instead.
Sometime between the events of Metal Gear Solid and Metal Gear Solid 2: Sons of Liberty, Liquid's arm was grafted onto Revolver Ocelot to replace the one that was severed by Gray Fox (as the Cyborg Ninja) at Shadow Moses. During the Tanker Incident, Liquid's mind appears to take over Revolver Ocelot's body. Liquid is the one who tipped off Solid Snake of the existence of Metal Gear RAY just before the Tanker Incident. The truth is that Ocelot used hypnosis, therapy, and special nanobots to mimic the personality of Liquid in order to fool the Patriot System. As Ocelot progressed, it became concerned that the manufactured personality of Liquid was controlling his actions. To regain his mind, Ocelot cut off Liquid's arm after the Big Shell Incident and replaced it with a cybernetic arm shown in the end of Metal Gear Solid 4: Guns of The Patriots . Although no longer under "Liquid's control", Ocelot continued to assume the role. Liquid died at Shadow Moses and the proof is that his ghost can be seen, in an easter egg, at Shadow Moses in Metal Gear Solid 4: Guns of The Patriots, Act 4.
- Following his appearance in Metal Gear Solid, Liquid was named the "Greatest Villain of All Time" by IGN.
- It is not made clear if Liquid Snake ever found out (whether as Liquid Snake or as Liquid Ocelot) that he inherited Big Boss' superior, dominant genes.
- Strangely, although Liquid has "all" the superior genes, he has blond hair, which in actual genetics, is characterized by a recessive (inferior) allele in the hair color gene. It is obviously possible he dyed his hair, though.
- According to the Cardboard Box trophy in Super Smash Bros. Brawl, Liquid is just as fond of cardboard boxes as his brother.
- When outside the control room of Metal Gear REX before Snake loses the PAL Card, the player can contact Liquid, who will still answer disguised as Master Miller, even though Liquid will appear to be sharing a conversation with Ocelot if the player looks at the control room in first person view.
- Killing enough human enemies in Metal Gear Solid 4 will cause Old Snake to have a flashback of what Liquid told him at the end of Metal Gear Solid ("You enjoy all the killing, that's why!"). The shock from this episode causes Snake to throw up and his Psyche Gauge lowers drastically.
- In MGS4, during the opening stage of the final battle with Liquid Ocelot, images of Liquid from MGS1 flash on the screen, and the "Encounter" music from MGS1 is played. Liquid Ocelot's attack patterns in this stage are similar to the ones Liquid Snake used in the fistfight on REX. The pre-fight cutscene also bears some resemblance to The Twin Snakes post-battle cutscene with Liquid.
- Liquid is the only one of the Snakes whose real name is never revealed, possibly because it was heavily classified.
- Liquid is the only Snake that has not worn an eyepatch (or a similar device).
- Liquid's back story of being captured in Iraq resembles the events of Bravo Two Zero, the ill-fated eight-man SAS patrol sent into the Gulf War.
- AbbyShot Clothiers, a company that creates media-inspired and video game clothing, created a trench coat similar to the one that Liquid wears. It is priced at $400 CAD, $343.14 USD, and £223.44.
- In the original plot for Metal Gear Solid 2, Liquid was supposed to have faked his death from FOXDIE. He was also going to be the actual main villain of the game. However, this, along with most of the original plot, was scrapped.