The full name of the security guard in the Half-Life series. Barney has Level 3 security clearance, which makes him useful for letting you into various parts of the base. According to the opening credits from Blue Shift, in the event of a disaster, Barney's first priority is "Preservation of Facility Equipment and Materials". Secondary priority: Protect staff. Of course, he's also responsible for personal safety, but really, that's not important.
In the game Half-Life, Barney was a blue suited man that could follow you around and open doors for you. He is extremely useful - he is an excellent marksman with his Glock and is good for drawing fire, if nothing else. Unlike the scientists, Barney will fight back if you harm him.
Barney was well-liked by Half-Life players. His various comments were, well, interesting at the least, and it was comforting to know he was there. Many gamers were saddened that they had to, at times, leave him behind or let him die. And so it was that Barney was given his own Half-Life expansion pack, Blue Shift.
Blue Shift wasn't considered to be too great by gamers, but I enjoyed it (short, though) and it tied in with the events of Half-Life and op4 nicely.