G-man

The G-man is a mysterious entity that appears many times throughout the resonance cascade.

Overview
The G-man appears to be a business man who teleports through out Black Mesa, carrying his suitcase everywhere he goes. He has talked to many inhabitants of Black Mesa, including Gordon Freeman, the Science Team, and Barney. At the end of Gordon's adventure, the G-man talks to him and invites him back to Black Mesa to reconstruct it and he creates a Chuck E Cheese's in which they all have a party at and celebrate the end of the resonance cascade.