Liquid Snake is Solid Snake's twin brother and genetic duplicate, along with field commander of FOXHOUND and the Genome Soldiers. Along with Solid Snake and Solidus Snake, he is one of three "brothers" genetically engineered from cell samples taken from Big Boss in the Les Enfants Terribles project. Liquid Snake believes himself as being inferior to Solid Snake, as he was told that he was the recipient of all of Big Boss' "flawed" recessive genes. Because of this belief, Liquid holds a strong resentment towards Solid Snake, who supposedly inherited the better genetics, and wishes to defeat him in combat and reclaim his what he felt was his birthright, thus proving his superiority.
Liquid is over 183cm tall, has an IQ of 180, and speaks seven languages fluently. He is an exact duplicate of Solid Snake in terms of appearances, with the only distinguishable feature being his darker skin tone and hairstyle (type and color). He also has a tattoo on his left arm, which resembles the Rod of Asclepius, but with a sword in its place. He sounds seemingly younger than Solid Snake as well as having a more British accent as well. In terms of personality, Liquid is shown displaying a more open, arrogant and loud attitude compared to Solid Snake, who is more cool, calm and confident.
Liquid Snake's Bio
Liquid was raised in the UK shortly after birth and was the youngest person to serve in the Special Air Service. During the Gulf War in Iraq, he was assigned to track down and destroy mobile Scud missiles. In truth, he infiltrated the Middle East as a sleeper agent for the British SAS, but was taken prisoner by Iraqi forces and held captive as POW until 1994, when he was rescued by the U.S. Government.
The Shadow Moses Incident and the FOXHOUND rebellion
Liquid Snake joined FOXHOUND in the year 2000, after Solid Snake and Colonel Campbell had already retired and left the unit. After Liquid joined, he became the field commander of FOXHOUND.
In 2005, he lead FOXHOUND as they seized Shadow Moses Island and the nuclear equipped Metal Gear REX, taking the DARPA Chief Donald Anderson and ArmsTech President Kenneth Baker as hostages. He then demanded the preserved remains of Big Boss in order to produce a cure for the genetic defects of the Genome Army. Basing himself in the Shadow Moses facility, and supported by FOXHOUND, the Genome Army, and Metal Gear's nuclear capabilities, Liquid intended to recreate Outer Heaven. With these vast resources at his command, Liquid would throw the world into the third world war, wanting to fulfill Big Boss' wishes of giving soldiers a means to carry out their way of life.
During the course of Snake's mission to eliminate the nuclear threat, he was confronted by Liquid on several occasions. Initially, Liquid attacked Snake from a Hind D attack helicopter, but retreated when his helicopter is crippled by the Stinger missiles fired by Snake. He survived (his parachute is visible on a tree in the Snowfield of the base) and then tricked Snake into activating REX with Kenneth Baker's PAL card by posing as McDonell Benedict Miller (who was dead at the time of the incident) during radio calls.
The entire final act of the Shadow Moses Island incident is a series of battles between Snake and Liquid. First, Liquid piloted the Metal Gear REX and attacked Snake, but, with the help of Gray Fox, Snake destroyed the Metal Gear. Then, Liquid and Snake battled bare-handed atop the ruins of the Metal Gear, attempting to fling each other from the top of the ruined mech to the ground far below. While it seemed Snake was victorious in this struggle, Liquid, manning a machine-gun-armed military jeep, pursued him as he tried to escape from the self-destructing Shadow Moses facility. Ultimately, Liquid fell victim to the genetically-engineered FOXDIE virus, just outside the facility.
Guns of the Patriots
Spoiler:
His influence did not stop with his death, however. He managed to posthumously take control of former ally Revolver Ocelot. However, some time following MGS2 but before MGS4, Ocelot removed Liquid's arm and replaced it with a cybernetic prothesis, cutting off Liquid's ability to possess him. Later, Ocelot underwent gene therapy and hypnosis to make him believe that he was Liquid Snake, in order to fool The Patriots into battling him while Big Boss' recovery was in process. It was not until the end of Solid Snake's mission that the Liquid persona gave way to the Ocelot persona and he revealed that he was in fact Liquid's double, signing off with a final hand taunt before dying. Big Boss, now fully recovered, later explained to Snake that Ocelot had volunteered himself to "transform" into Liquid Snake, allowing Big Boss to live again.