Who do you think the Gman is ? :spolier possibility:

[sam_justice]

I think that the G-man is an alien, he can take human form and use the world as he wishes, since you dont see him at the begining of hl2, he was teleported in by Gordon, thats why he values his life and watches him a lot, he knows that he bought him here (for a reason we do not know) but he has something he wants to clear up

 

[Splinter16]

He was there long before the cascade, so he wasn't excatly teleported in. It would appear from the end of HL2 that he can maniplate time to his wim, so possibly he's from a future invester, who wish to find the prefect assissan, maybe Gordon orginally got killed escaping from black mesa, and the G-man was sent to change the turn of events to Gordons favour. Which is why you see him talking to everyone.

 

[sam_justice]

hmm yeh

 

[destrukt]

http://www.halflife2.net/forums/forumdisplay.php?f=78