John Carmack is an American computer-game designer whose pioneering work on three-dimensional game design led to the popularization of the “first-person shooter” genre, exemplified by such popular games as Doom and Quake. His company, id Software, developed shareware and Internet distribution channels, revolutionizing how computer games were sold.

Softdisk, a computer company in Shreveport, Louisiana, hired Carmack to work on Softdisk G-S (an Apple IIGS publication), introducing him to John Romero and other future key members of id Software such as Adrian Carmack (not related). Later, this team would be placed by Softdisk in charge of a new, but short-lived, bi-monthly game subscription product called Gamer's Edge for the IBM PC (DOS) platform. In 1990, while still at Softdisk, Carmack, Romero, and others created the first of the Commander Keen games, a series that was published by Apogee Software, under the shareware distribution model, from 1991 onwards. Afterwards, Carmack left Softdisk to co-found id Software.

Carmack has pioneered or popularized the use of many techniques in computer graphics, including "adaptive tile refresh" for Commander Keen, raycasting for Hovertank 3-D, Catacomb 3-D, and Wolfenstein 3-D, binary space partitioning which Doom became the first game to use, surface caching which he invented for Quake, Carmack's Reverse (formally known as z-fail stencil shadows) which he devised for Doom 3, and MegaTexture technology, first used in Enemy Territory: Quake Wars. Carmack's engines have also been licensed for use in other influential first-person shooters such as Half-Life, Call of Duty and Medal of Honor.

At one point in time, Carmack was described as having “no empathy for other human begins”. The man is well known for coming into work at early hour, getting everything done and then repeating the process (to the tune of 80 hours a week). They said his idea of a vacation was to take his computer to a hotel, isolate himself from the world and just code for a week or two. Carmack settled down and married Katherine Anna Kang in 2000 (Kang was renowned for the mobile games she created for id Software including Doom RPG and Orcs & Elves which were critically acclaimed), and of course Carmack had to bring his workstation along when they went on their honeymoon.

During the early days of id Software, John Romero found himself locked in his office. The solution would have been to simply call the handy man but John Carmack at the time observed the door and decided to use a battle axe on it instead. Yes, a friggin’ battle axe and not just any battle axe either – this was a $5000 custom made battle axe. The door was chopped down much to the joy of the staff at the time and the door itself remained in pieces for a good while afterwards.

Carmack as well – he pursued college for two semesters before dropping out and becoming a freelance games developer. Of course, it’s another matter that Carmack broke into his school at the age of 14 to steal some Apple II computers using thermite and Vaseline.

Carmack had always expressed an interest in unorthodox and far-flung ideas like space tourism. To further that dream – and to make use of the millions in his possession – Carmack founded Armadillo Aerospace. The organization started working on manned suborbital spacecraft and won various challenges in 2008 and 2009 for its work. In August 2013 however, the company would be placed in “hibernation” and subsequently acquired in early 2015 by former employees who began Exos Aerospace. While Carmack did dream big, Armadillo Aerospace is one example of things not quite working according to plan.

On August 7, 2013, Carmack joined Oculus VR as their CTO. On November 22, 2013, he resigned from id Software to work full-time at Oculus VR. Carmack's reason for leaving was because id's parent company ZeniMax Media didn't want to support Oculus Rift. Carmack's role at both companies later became central to a ZeniMax lawsuit against Oculus parent company Facebook, claiming that Oculus stole ZeniMax's virtual reality intellectual property. The trial jury absolved Carmack of liability, though Oculus and other corporate officers were held liable for trademark, copyright, and contract violations. In February 2017 Carmack sued ZeniMax, claiming the company had refused to pay him the remaining $22.5 million owed him from their purchase of id Software.

Carmack is a well-known advocate of open source software, and has repeatedly voiced his opposition to software patents, which he equates to "mugging someone". He has also contributed to open source projects, such as starting the initial port of the X Window System to Mac OS X Server and working to improve the OpenGL drivers for Linux through the Utah GLX project.

. Carmack released the source code for Wolfenstein 3D in 1995 and the Doom source code in 1997. When the source code to Quake was leaked and circulated among the Quake community underground in 1996, a programmer unaffiliated with id Software used it to port Quake to Linux, and subsequently sent the patches to Carmack. Instead of pursuing legal action, id Software, at Carmack's behest, used the patches as the foundation for a company-sanctioned Linux port. id Software has since publicly released the source code to Quake, Quake 2, Quake 3 and lastly Doom 3 (including, later, the BFG Edition), all under the GNU General Public License (GPL)

The Doom source code was also re-released under the GPL in 1999. The id Tech 4 engine, more commonly known as the "Doom 3 engine", has also been released as open source under the GPL. The source code for Hovertank 3D and Catacomb 3D (as well as Carmack's earlier Catacomb) was released in June 2014 by Flat Rock Software with Carmack's blessing. On the other hand, Carmack has several times over the years voiced a skeptical opinion about Linux as a gaming platform for instance in 2013 he argued for emulation "as proper technical direction for gaming on linux" and in 2014 he voiced the opinion that Linux might be the biggest problem for the success of the Steam Machine.

Carmack contributes to charities and gaming communities. Some of the recipients of Carmack's charitable contributions include his former high school, promoters of open source software, opponents of software patents, and game enthusiasts. In 1997, he gave away one of his Ferraris (a 328 model) as a prize to Dennis Fong, the winner of the Quake tournament "Red Annihilation".

As a game developer, he differs from many of his contemporaries by avoiding commitment to a final release date for any game he is developing. Instead, when asked for a release date on a new title, Carmack will usually reply that the game will be released "when it's done."

During his time at id Software, a medium pepperoni pizza would arrive for Carmack from Domino's Pizza almost every day, carried by the same delivery person for more than 15 years. Carmack had been such a regular customer that they still charge him 1995 prices. As you can see you can be part of the gaming business and not be a suit-wearing guy worrying only about the sales.