Cpl. Adrian Shephard is the protagonist of Half-Life: Opposing Force, a US Marine Corporal assigned to the Hazardous Environment Combat Unit from the Santego Military Base in Arizona, where he was trained by Drill Instructors Dwight T. Barnes and Sharp. During the Black Mesa Incident, he is one of the men sent to the Black Mesa Research Facility to kill the Xen invaders and later silence the witnesses, especially a scientist named Gordon Freeman, as part of a classified mission. Early in the game, Shephard finds himself separated from his unit and ends up fighting solely for his life, aided by fellow Marines scattered around the facility and Black Mesa personnel, and in addition to the Xenian invaders confronts another alien faction, Race X, and the Black Ops, who become much more prominent enemies during the events of Opposing Force in comparison to the other games in the series. He was 22 years old at the time of the events.
from the combine overwiki page on Adrian Shepherd.
Adrian Shepherd my beloved 
God I want an MP5A3 so god damn bad… and to have a cosplay of this dude so bad… I wanna be Adrian… so freakin bad.