You've got to go back to the 90s to truly appreciate how influential Carmack was and how he single handedly drove Microsoft to the Xbox.
It is official. John Carmack, probably the greatest game developer of his generation, is leaving iD Software, the iconic company behind Quake and Doom, that he co-founded.
Carmack was 21 years old when he co-founded iD Software. He pioneered 3D graphics techniques that are still in use to this day and if you ever get a chance to play Wolfenstein 3D, and are under 30 years old, you may not realize how much of an impact it had on people's perception of the personal computer.
For a long time, until the advent of VGA graphics, personal computers lagged game console in graphics capabilities. By the time the first 3D graphics chips were hitting the market in the mid-90s, the PC was ascendant. It didn't take much work to drop $4-5,000 on a high-end gaming rig to play in weekend Quake tournaments at LAN parties.
Carmack was so influential that when he decided to opt to use OpenGL programming APIs to drive 3D graphics hardware on Windows PCs, over Microsoft's own Direct3D APIs, the engineering staff in Redmond would be cowed by the threat to their platform, perceived or not.
And Carmack didn't budge even with the onslaught of courting, and marketing that Microsoft put behind DirectX. He was quite clear that Direct3D was inferior to OpenGL, and he had the goods to prove it: Quake and Doom were examples of what was possible on PC 3D hardware. They were the standard by which other 3D games were judged, not only in terms of gameplay, but in pure terms of pure technology.
It was Carmack who also gave his seal of approval to the PlayStation. Microsoft, threatened by the potential of consoles to encroach on its home computing turf, first worked to develop a console in partnership with Sega, the Dreamcast, and when that didn't pan out as they hoped, they jumped full bore into the market with the Xbox.
Always, the standard bearer for excellence for the software coming out of iD Software.
Now, Carmack is CTO of Oculus Rift, and he is putting his prodigious intellect behind enabling virtual reality experiences in a mobile environment. It seems like the logical path for him to take, but it also means the end of an era, the PC era.
Was Carmack really that influential? Yes, he was. Not always available, and not always easy to understand, but he did things his way, stayed the course, and made everyone around him adapt. He had both the creative and technical skills and he delivered the goods. He is still waging the good fight as he stands up for AMD's Mantle API.
Alex St. John, one of the original developers of DirectX at Microsoft has a nice take on what happened between Carmack and Microsoft here.
Ed Fries, who led the original Xbox team at Microsoft has his version of how the console came into being here.