It's no secret that Valve scanned the faces of real people to use as 3D meshes for characters in Half-Life 2. Most of them are credited in the "Thanks to the following for the use of their faces" section of the credits in Half-Life 2 and its follow-up episodes. Thanks to Source Filmmaker and Garry's Mod, many of them have enjoyed a memetic life beyond the Half-Life series too, with even the background citizens of City 17 developing followings in the SFM community.
YouTuber Richter Overtime did some digging to find out where the people behind those faces are now. Some are already well-known to Half-Life fans, like Jamil Higley, the actor and model who was scanned to create Alyx and also performed her motion capture (according to IMDb, she also did mocap on No One Lives Forever). But there are plenty more you might not know.
For instance, Father Grigori, the shotgun-toting priest Gordon meets in Ravenholm, was based on Daniel Dociu, who was the art director for Guild Wars and Guild Wars 2. He ended up in the role because his son, Horia Dociu, was an environment artist on Half-Life 2.
While many of the citizens in Half-Life 2 are based on actors, Valve employees, their partners, or random people they found around Seattle with interesting faces, one is more unusual. The model for Male_03, who holds the door while you escape to the rooftops during the Combine raid at the start of the game, was based on producer and DJ Larry Heard. Under the name Mr. Fingers, Heard released singles that helped define Chicago house music like Can You Feel It? How he ended up in Half-Life unfortunately isn't recorded.
Richter Overtime had trouble tracking down Male_07, better known to me at least as Gordon Frohman, star of Chris Livingston's webcomic Concerned. He's credited as "Michael Smith" and that's not an easy name to find. After recording the video, he did manage to learn a little more about Smith. Apparently the face of Gordon Frohman "welds planes together now so my boy is making some serious dough". Good for him.
In a previous video, Richter Overtime highlighted a grimmer story behind one of these faces. The photograph scanned for "corpse01.mdl", which appears as a dead body in Half-Life 2 and has been adopted by the GMod community as the "Hobo" career on DarkRP servers, is based on a photo of a real corpse from a medical textbook. It's not uncommon for videogame artists to reference photographs of injuries, but it's odd to think the burned face seen in a videogame belonged to an actual person. YouTube commenter thezackattack5328 adds, "Something even more creepy is this model in specific is used as Reference for scale in Hl2 maps. So if you port a Gmod or HL2 map into SFM and turn off lighting, since it's not a TF2 map this model will just randomly appear and disappear while you're animating. Talk about a Ghost In The Machine😬"