The Machinegun Kid was an Outer Heaven mercenary sent to stop Solid Snake during his first mission in 1995, acting as a minor antagonist in the original Metal Gear.
The Machinegun Kid was formerly an SAS (Special Air Services) commando who specialized in fully automatic firearms, giving birth to his codename. Always wielding a machinegun in his hand, the Machinegun Kid eventually stopped his soldiery in the SAS and joined Outer Heaven as a mercenary.
Once FOXHOUND rookie Solid Snake intercepted Outer Heaven to save his colleague, Gray Fox, under the command of Big Boss, he encountered the Machinegun Kid whilst exploring the corridors of the base. As the Machinegun Kid was stationed to stop anyone from passing, a battle ensued between the two troopers, but Snake came out on top and killed his rival in a firefight.
Metal Gear Solid: Portable Ops
Metal Gear Solid: Peace Walker
Metal Gear Solid V: Ground Zeroes
Metal Gear Solid V: The Phantom Pain
Metal Gear 2: Solid Snake
Metal Gear Solid
Metal Gear Solid 2: Sons of the Liberty
Metal Gear Solid 4: Guns of the Patriots
Metal Gear Rising: Revengeance