Hilde Garn is the main antagonist of Metal Slug: 1st Mission, acting as the final boss.
This warrior is an expert at guerrilla warfare and is the key target of the 1st mission. He's gathered an arsenal of weapons in secret and is believed to be the ringleader of the mysterious activities taking place in the army and has even had a hand in the development of new weapons.
Hilde Garn has a heavy resemblance to Donald Morden (complete with an eyepatch). Once the hat is taken off, his bald spot stands out.
Hilde Garn appears in the game's final mission patrolling the Facility Elevator and the Rebel Truck. Inside the Rebel Truck is a large personalized Slug. The Slug contains a Vulcan, a container full of homing missiles, and it's able to do a Metal Slug Attack without self-destructing.
The fight with Hilde Garn and his Slug takes place on the Rebel Zeppelin. After the Hero disposes of the Slug, Garn falls to his apparent death. Garn's Slug shows up again in Metal Slug: 2nd Mission but not the man himself.