I worked with Gabe and team to develop the "guy in the logo" back when we first named the company, Valve (circa 1995/6), and needed to develop the visual brand vocabulary to go along with it.
Interesting that you should ask about the bald guy. Back then, the casting agencies we were using to find models only had "supermodel"-type talent. We kept requesting "heavy-set", "normal" models, and they kept sending us "beautiful", "thin", "perfect" headshots to review.
So, we finally asked them to just go out on the street and pull "everyday Joes" who were more "interesting", "common", and for the bald guy, "kinda big, heavy-set, and bald".
They went out to the streets of Seattle's Broadway district, took tons of polaroids of the types of folks we were looking for, and brought the shots back to us. We selected the bald guy from the batches of "off-the-street" polaroids—he was literally pulled out of a coffee shop or book store!
A few days later, we brought him into studio and shot the image you now see at the beginning of our games. We also shot a 2nd image of a different guy with a valve in his eye using the same process (you might remember him as well—attached below). The two comprised the "Open your mind. Open your eyes." concept for our initial brand, respectively.
It's been very long since we did that work, so we don't know who the models were. And the fact that they weren't professional models, would make it very difficult to find them—if not impossible for the bald guy (not facing camera).
My fellow bald people, lift your heads high not just to be seen, but also because you ARE seen! :-)