- "What's your name, dirtbag? Sound off like you got a pair! Corporal Shephard, huh? Looks more like Corporal "Dog Meat" to me! Seems your name was mysteriously bumped to the top of the advanced training list!"
- ―Dwight T. Barnes in 1344
Corporal Adrian Shephard is a 22-year old (by the time of the Black Mesa Incident) US Marine Corporal assigned to the Hazardous Environment Combat Unit from the Santego Military Base, Arizona, where he was trained by Drill Instructors Dwight T. Barnes and Sharpe.
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. 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 employees.
After he managed to defeat the Race X forces, the Gman place Shephard in status where he did not wake up until 1372, a full two years after the City 17 Revolt and start of the Golmar Uprising, he then aided a group of former world military soldiers, some of which used to be his old comrades in arms, that was established by the Combines from the remnant of the world's military (largely American, Russian, Korean, British, French, German, Japanese, Canadian, Vietnamese, Australian, New Zealander and South African) that haven't been either killed or converted into first gen TransHuman Combine Soldiers and combined into a group refereed to simply as the Global Defense Force or GDF, which were regulated to simply containing Antlions or Headcrab/Zombie infestation and other, rather minor operations, but which the uprising went fully underway, the GDF quickly sided with the Resistance and proceeded to fight the now weakened Overwatch forces that's now stranded on Earth. Over time, he reencountered Gordon Freeman, the now famously known as 'The One Free Man' and hero of the uprising. Although the two started off on the wrong foot, the two begrudgingly agreed to help each other out and over the course of the Uprising and following Civil War, the two became good allies. As of now, Shephard, now a General within the Human-Vortigaunt Federation, is now one of the Alliance biggest war-heroes on par with Gordon Freeman in sheer amount of almost deification by many Allied soldiers