It would appear that another veteran employee from Valve has left the company. According to two sources, Valve's employee page and LinkedIn, John Cook may have left Valve about a month ago after working there for 17 years. You can see which strings were removed from Valve's employee page by going to SteamDB's SteamTracker. John Cook is the co-founder of the original Team Fortress (along with Robin Walker) and was one of the head developers of Steam since the early days of Half-Life 2. If this means that he has left the company, John Cook would be known to be the fourth veteran employee of Valve to leave within the last twelve months, following Ted Backman, Marc Laidlaw, and Doug Wood. Kudos to the Facepunch and NeoGAF communities for spotting this.