Mass Produced Biomechanical Unmanned Mecha

A fan group for the Gekko in Metal Gear Solid 4: Guns of the Patriots. Gekko means Moonlight in Japanese.

The Gekko are fictional large unmanned autonomous fighting vehicles developed by AT Corp for use in ground combat. Officially designated IRVING by the United States Army, Gekko are colloquially called "lizards" after the species of small lizard with a similarly spelled name: gecko. These war machines were created using a combination of technologies used in the production of Metal Gears REX and RAY. However, Gekko are not Metal Gear. Unlike true Metal Gear, Gekko have no nuclear launch capability. Instead they are more akin to infantry fighting vehicles, with multiple units acting as a coordinated team in support of ground forces.

A Gekko has a large mechanical turret-like head whose shape gives the impression of a distinct face and snout. This is connected via a neck to a smaller body at the back of which are two large, hip-like structures. Like the head, the neck, body and hips are mechanical. All are connected via mechanical movable joints. The joint connecting the head to the neck allows the head to turn 360 degrees. Attached to the hips are are pair of very strong legs with three-toed clawed feet and a single large opposable claw on each heel. The legs are encased in a protective rubber-like substance. These legs, unlike the head, neck, body and hips, are biological, save for the claw on the heel. The legs internal muscle fiber are composed of artificially created muscle tissue cloned from the stem cells of ungulate/bovine embryos. Gekko walk on their toes nails. Because each hip is connected to the body via a universal ball joint, a Gekko's legs have a very large range of motion. The central front area of the hips have a warning sign forbidding anyone from trying to strike at this area.

As Gekko's legs are made up of highly flexible artificial musculature that mimics living flesh. It rapidly builds up lactic acid that occurs when they move. The "urination" we see in game is the Gekko expelling the build up of lactic acid in their legs. Gekko commonly piss mainly in groups so all units are combat ready at same time.

Being bio-mechanical, a Gekko has a circulatory system that uses blood to nourish its legs. If cut or shot, its legs bleed.

Wikipedia Article[metalgear.wikia.com]
Combat Capability Video