Artist Viktor Antonov has worked on a number of high-profile projects over the years. He's recently published his own book, The Colony. He's helping on a live-action adaptation of classic manga (and anime film) Cobra. He also did some nice art for shelved (yet promising) multiplayer shooter The Crossing.
Oh yeah. And he was also art director on Half-Life 2.
During his time with Valve, Antonov created much of the iconic imagery we associate with the game, including the look of City 17 (and environments beyond, some of which were cut, others which returned in HL2 spin-off The Lost Coast) and the vehicles and equipment of the Combine.
If you're after something a little more current from the man, he's working on Bethesda's upcoming Dishonored. You can find more of his work at his personal site, linked below.
Viktor Antonov [vulkanbros]
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