December 2004 – May 2017
Faliszek is the co-writer, along with Marc Laidlaw and Erik Wolpaw, of the Half-Life 2: Episode One, Half-Life 2: Episode Two, and Portal stories. He also wrote the story for Left 4 Dead, and later co-wrote Portal 2’s plot with Wolpaw and Jay Pinkerton.
Faliszek is, with Wolpaw, the creator of the now defunct website Old Man Murray. He shared an office at Valve with Wolpaw and Laidlaw until he left the company in 2017. Laidlaw once stated on his personal blog that "for years, Chet and Erik were legendary figures of mythic status to me. They still are, except now I can throw things over my shoulder and hit them." On Valve's official website, Chet's function was described as follows: "We are all still trying to figure out exactly what it is that Chet does at Valve, but at the very least he occupies office space on the 11th floor as self-proclaimed Mr. Awesome."