Unmanned bipedal walking weapons manufactured by AT under the project name "Irving". Nicknamed after the gecko lizard. Designed for urban combat, they are capable of both accompanying and cooperating with food soldiers as well as autonomous patrol. They are equippable with a variety of mission-appropriate combat units, including an internal nuclear warhead. Because they aren't always used for nuclear warfare, they escape traditional definition of a Metal Gear. Produced en masse, they represent the core weaponry used in contemporary warfare. There are now more Gekko in service than there are tanks.

At the core of their design lies the ability to retain a high degree of mobility, even in tight and windy areas such as the urban landscape. Gekko were built to be as small as possible in order to allow tactics including the solo infiltration and demolition of buildings by traveling unmanned to its core, even via large service elevators, and self-destructing.

In order to achieve maximum responsiveness and secure a high power-to-weight ratio, its primary drive comes from its two legs, composed of artificial muscle made by genetically altering ungulate clone ES cells. Retaining the unparalleled swiftness and dexterity innate to its hyperathlete legs, however, required that they be comparatively lightly shielded, making them the Gekko's weak point.

The central computer unit housed inside the Gekko's head is encased in heavy armor, allowing it to demolish buildings with a headbutt.

Its target acquisition and firing systems rely upon an electro-optical (EO) sensor and a television camera system that registers both visible and infrared spectra, rendering optical stealth camouflage ineffective. Environmental camouflage like OctoCamo offers better results. The Gekko are also equipped with sound and vibration sensors, enabling it to detect footsteps.

Its tentacles house composite sensors for scanning the immediate area. In addition to detecting living organisms, they can also be used as powerful whips in close-range combat.

When inactive for extended periods, they enter a hibernation mode in which the internal battery sleeps and all biological parts are protected.