Valve is currently celebrating the 25th anniversary of its iconic first-person shooter Half-Life, and as part of this, it's released a lengthy documentary discussing the entire history of the project. It also happens to have a segment touching on the co-founders' departure from Microsoft.

This includes both Gabe Newell and Mike Harrington, with the documentary going into detail about how the pair had to prepare themselves. Both of them thought there was a good chance they would be asking for their jobs back at Microsoft after about a year:

Gabe Newell: "On the surface, we should have failed, and realistically, both Mike and I thought we would get about a year into it, realise we'd made horrible mistakes and go back to our friends at Microsoft and ask for our jobs back. But we did think that we knew a fair bit about software development, that there was expertise that goes into it. I think we also had some pretty clear ideas of how to design a company, right? So when we were building Half-Life, we were also designing Valve at the same time.

Harrington goes into some extra detail about how his friend and former Microsoft colleague Michael Abrash (Quake) linked up with John Carmack (Commander Keen, Wolfenstein 3D, DOOM, Quake) at id Software, which played a part in Valve's success:

Mike Harrington: "I wasn't really used to big companies. When I started at Microsoft, it wasn't that big. It was like 1500 people, like a big high school. Nine years later it was significantly bigger. And I was like, oh, this place is too big. And, you know, that was still like 1996. So they had long ways to go. I told my managers like a year before, like, I'm leaving. I'm leaving in a year, and I'm gonna start a game company. And the first person I talked to was a good friend of mine, Michael Abrash. But at that time, he was trying to do something within Microsoft. And by the time it made sense, John Carmack had convinced him to go work at id, so how could he say no to that? And then I was having lunch with Gabe and I said, Gabe, I'm leaving, I'm just gonna leave, and I'm gonna start a game company. He goes, I wanna leave, I wanna start a game company. I go, alright. And that was it."

This eventually led to id Software's co-founder John Romero guiding Newell and Harrington on "how to start a game company" - with Valve also walking away with the source code to Quake, and in Mike's words it was "game on" from there.

Valve and Microsoft have unsurprisingly maintained good relations over the years, with Valve porting its titles to multiple Xbox systems in the past and Microsoft also offering its games on the Steam service via PC. If you are interested in learning more about the history of Valve and Half-Life, the above documentary is well worth a look. Half-Life is also available for free this weekend on Steam.