CVG:

"How did the G-Man come about, then?

Marc Laidlaw: I remember Ken Birdwell came into my office and he'd been thinking about all the The guy who puts story in front of the crowbar different functionaries you'd have in an institution like Black Mesa. You have your scientists and their administrators - the tax guys, the government guys who are checking over the books and representing some other interest - and you're not quite sure who they are.

The original concept was born from that and we developed from there. 'What does he do?' 'Well, he's not actually a combat character.' 'So what happens when you shoot him?' 'Well, it turns out you actually can't kill the guy.' 'So what does that mean about him'?"