This article is about Gear REX, as featured in the Metal Gear SolidMonster Hunter tie-in. You may be looking for the bipedal mecha Metal Gear REX, after which it was modeled.
This article is about a non-canonical topic in the Metal Gear series.


Gear REX.

Gear REX (ギア・レックス Gia Rekkusu), also known as the "Nuclear Dragon/Steel Fanged King," was a monster that Big Boss and the Militaires Sans Frontières encountered during the Peace Walker Incident.


Gear REX was created due to mutations from nuclear test sites. Because of the mutations, Gear REX developed a protuberance resembling a gun–turret, as well as a highly acidic and corrosive mucous that is capable of melting absolutely anything it comes into contact with. However, the mucous can be reverse-engineered to form a highly flexible and sticky substance. When creating the substance, its bodily fluids are turned into a purified form via filtering them, which results in it becoming incredibly concentrated. Further distillation of the filtered bodily fluids from Gear REX will increase the concentrated state to devastating levels. It is also capable of ejecting the spines on the side of its head and its roar can vibrate the spines and cause them to shatter, which is effective in stunning its prey.


Gear REX performing a roar.

Gear REX was first spotted on Isla del Monstruo, although it was presumably not native to the island, since there was no record of any nuclear tests having been carried out in the region. Sometime afterwards, a Gear REX originating from the Pacific entered Costa Rica from the South Pacific coast and traveled to Mt. Irazu, until it reached the crater's vicinity around noon the next day and stopped, destroying several houses and buildings in the process. Because Costa Rica had abolished its army after the Costa Rican Civil War, it was unable to deal with Gear REX, and thus the MSF was dispatched to stop it.

Sometime after both the prior event and Big Boss's battle with Paz Ortega Andrade and ZEKE, a Gear REX somehow managed to board MSF's Mother Base and caused some havoc. Because of this, the MSF had to go on the defensive and defeat Gear REX.

Sandinista comandante Amanda Valenciano Libre once commented on feeding Somoza to Gear REX during Big Boss's fight against the monster. Her brother Chico told Big Boss of a legend that Gear REX was a dinosaur that had been revived as a zombie and attacked people, with Big Boss expressing disbelief in the existence of zombies. Chico counters his argument by stating that Haiti plantations had used zombies as slaves for years, and had even handed down a secret zombie powder over many generations.


The Gear REX is shown to be a very vicious predator, frequently emitting a high-pitched roar. Aside from its protuberance emitting a stream of acid (which it can do in an arc or in a straight line), the Gear REX also attacks by charging at an enemy (although in rare times, it also trips when it reaches a certain distance), and can even emit a drawn out high-pitched roar that can stun nearby enemies, and it can eject the spines from its head to use them as both projectiles and a means to amplify the sound of its roar to stun its opponents from afar. At times, it also tends to stand in place and stamp down erratically as if throwing a tantrum. In rare cases, it can even do a sideswipe via its body as well as use its protuberance to peck at the ground and spin around and use its tail like a whip.

Behind the scenes

"A mysterious member of the dragon family, also known as the "nuclear dragon." Although it lacks wings and cannot fly through the air, a sudden mutation brought on by nuclear testing has given it a giant protrubence reminiscent of a gun turret, from which it spews a highly corrosive liquid that melts absolutely anything."
―Gear REX description in Metal Gear Solid: Peace Walker

Gear REX on Isla del Monstruo.

Gear REX is featured in the non-canonical Monster Hunter Extra Ops in Metal Gear Solid: Peace Walker. It bears a strong physical resemblance to its namesake, Metal Gear REX, including bone ridges that make its face look like the Metal Gear, and a limb over its right shoulder representing the rail gun.

Gear REX's creation, as a result of nuclear testing, resembles that of the famous Japanese movie monster Godzilla (known as Gojira in Japan). In Metal Gear Solid 3: Snake Eater, Para-Medic discusses with Naked Snake the movie Godzilla and its status as an anti-nuke movie; the eponymous monster being symbolic of the dangers of nuclear power. Big Boss jokingly remarked that the Marshall Islands must be, "crawling with creatures like Godzillia," due to nuclear testing.

Despite the fact that Gear REX was created as part of a crossover between the Metal Gear Solid and Monster Hunter franchises, Gear REX's bio does not contain the latter's trademark, as it is a unique monster made for the crossover. Likewise, it's also the only "Monster Hunter" creature to be fought in areas besides Isla del Monstruo. Similarly, Gear REX's bio has a mistake in it where it spells Gear REX's name as "Gear Rex" instead of "Gear REX."


Defeating Gear REX with an S-rank on any Hunting Quest (EXTRA Ops 125-128) will unlock the Gear REX uniform, which will allow anyone who wears it to steal PSYCHE energy from the enemy.

Completing Gear REX Strikes Back (EXTRA Ops 128) for the first time will unlock the Cookbook research document for development. The Cookbook affects monsters in the same way as Magazines do to soldiers, leaving the distracted monsters open to attacks.

Defeating Gear REX is essential to constructing the Human Sling Shot. Each encounter with Gear REX has a chance to unlock research items that allow of the development of the Sling Band component. Like in Monster Hunter breaking off pieces of Gear REX will cause rare items to drop after the mission. S-Ranking any Gear REX Hunting Quest after breaking off her horns, back spines, tail, and the red sack below the laser arm almost guarantees a research item unlocking.

Rare Item Unlocks and Weapon Development

Below are the items that have a chance to unlock after each Hunting Quest and the weapon can be developed once the item has been unlocked.

  • Sling Band Rank 1 - Gear REX Mucous -> EXTRA Ops 125 and 126 (Gear REX Hunting Quest and Gear REX Twilight)
  • Sling Band Rank 2 - Gear REX Concentrate -> EXTRA Ops 127 (Gear REX Showdown at Craterbase)
  • Sling Band Rank 3 - Gear REX Super Extract -> EXTRA Ops 128 (Gear REX Strikes Back)

Gear REX making a slow approach.

If the player attempts to scan Gear REX with the Analyzer, it will list it as "Unknown."

Unlock Items

Gear REX Mucous

Highly acidic liquid fired out by Gear REX . Can be modified to form a powerful sticky solution.


Side view of Gear REX.

Gear REX Concentrate

Gear REX's bodily fluids filtered to increase purity. Incredibly concentrated.

Gear REX Super Extract

A distilled version of Gear REX's filtered bodily fluids, increasing the concentration. Devastatingly concentrated.

Gear REX (Uniform)

Gear REX Camouflage

Variation of Jungle Fatigues camouflage. Grants the wearer the ability to steal PSYCHE from enemies after grabbing them.

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