12 Things You Didn't Know About Half-Life 2
4. Valve Used Real People As Reference Models
It may seem like common practice these days to base characters off real actors for AAA games, something especially true with the rise of motion-capture technology, and it's often used to create the most realistic graphical experience possible, but it wasn't always the case.
Back in the early 2000s, it was still uncommon for developers to take this approach, often creating characters from the ground up instead and being 'inspired' by actors (but keeping the models different enough to not get sued). Valve decided against that approach and hired a number of actors, utilising their faces for character textures.
Whilst they certainly weren't major actors, Valve hired Frank Sheldon for G-Man, Roger Guay for Wallace Breen, Jamil Mullen for Alyx Vance and more. It’s a small detail but one that helped give life to HL2's cast, making them seen human.