John Carmack (born August 20, 1970) is a game programmer and co-founder of id Software. He is personally responsible for a number of significant enhancements and breakthroughs in computer graphics which have now become commonplace.

Carmack grew up in the Kansas City Metropolitan Area. He has said of himself as a child, "I was sort of an amoral little jerk when I was young. I was arrogant about being smarter than other people, but unhappy that I wasn't able to spend all my time doing what I wanted." What he wanted to be doing was programming computers. He has stated that he knew from the age of 12 that he wanted to work with computers, but at that time his opportunities to work with them were scarce. When he was 14, Carmack and some friends broke into a school to steal Apple II computers and were caught, for which John spent a year in a juvenile home.

After finishing high school, Carmack studied computer programming for two semesters at the University of Missouri–Kansas City, but dropped out. "It just didn't seem all that worthwhile," Carmack later said. "In hindsight, I could have gotten more out of it than I did, but I hadn't acquired a really good attitude towards learning from all possible sources yet." Carmack worked as a freelance programmer for a time, but found making money difficult. He was then hired by Softdisk, a company based in Shreveport, Louisiana, to program games for their monthly subscription service. It was at Softdisk that he met future id Software co-founders John Romero, Adrian Carmack (no relation), and Tom Hall.

It was also at Softdisk that Carmack developed the graphical breakthrough which would be instrumental in the creation of his first successful game. Carmack came up with a method that allowed PCs to mimic the smooth scrolling of so many console platform games of the era. Tom Hall, John Romero and John Carmack used this new technique as the foundation for Commander Keen, a side-scrolling platforming game which was distributed as shareware by Apogee Software (currently 3D Realms). In the wake of Commander Keen's considerable success, Carmack, along with Tom Hall, John Romero, and Adrian Carmack, departed Softdisk to form id Software, which was officially founded on February 1st, 1991.

An early id game, Hovertank 3D, is referred to by id's website as "the first 3D PC game ever!" This claim is open to dispute, but Hovertank 3D was certainly noteworthy for its graphics engine. With it, Carmack pioneered a technique in which the computer would only render the area which was visible to the player, rather than the entire level. This conserved processor power, which could then be devoted to more detailed graphics. This technique was instrumental in the later creation of the first extremely popular first-person shooter, Wolfenstein 3D, which was released by id on May 5, 1992. Carmack and id would follow up the success of Wolfenstein with Doom in December of 1993.  Doom was powered by Carmack's Doom engine, also known as id Tech 1. This same engine powered the sequel, Doom II, which was released in October of 1994.

For 1996's Quake, Carmack developed another engine, the Quake engine, which represented another significant step forward for first-person shooters. The engine allowed for preprocessing and pre-rendering of the 3D environment, reducing the amount of processing and improving overall speed and performance, and brought with it innovations in lighting as well.

Carmack continued to develop game engines for id games, designing id Tech 2 for Quake II, id Tech 3 for Quake III Arena, and id Tech 4 for 2004's Doom 3, which featured unified lighting and shadowing.

His most recent engine is called idTech 5, and will be used to power Doom 4 and Rage, a game currently in development for PCs and consoles which will combine driving and shooting action in a post-apocalyptic, Mad-Max-inspired setting.

Carmack is an advocate of open source. He has made id Tech 1, 2, and 3 available for download and has stated that eventually id Tech 4 and id Tech 5 will be open source as well. He is opposed to the notion of software patents, saying, "The idea that I can be presented with a problem, set out to logically solve it with the tools at hand, and wind up with a program that could not be legally used because someone else followed the same logical steps some years ago and filed for a patent on it is horrifying."

He is also known for refusing to provide projected release dates during game development, frequently responding to inquiries about when a game will be released with, "When it's done."

Carmack has also dabbled in the development of mobile titles. He was frustrated with what he saw as the poor quality of mobile games after receiving a cell phone from his wife, machinima producer and Fountainhead CEO Katherine Anna Kang. He has since worked to develop two successful mobile games, Doom RPG and Orcs & Elves.

He is driven more by a love for programming itself than a love for games, saying in a 2000 interview, "In the gaming industry, there are a lot of people that are specifically in it because they love games and they want to create things. My love for programming is a more abstract thing. I'm taking a great deal of enjoyment writing device drivers for Linux. I could also be having a good time writing a database manager or something because there are always interesting problems. There are some things that are inherently more rewarding than others. Graphics and games are probably the most generally rewarding area of programming."

He also spoke, in the context of Quake 3, about his philosophy surrounding designing games, and what he feels sets him apart from a number of other designers. "Specifically what we set out to do with Quake 3 was just a completely eyes-wide-open-focus on the game just being fun while you're playing it. There's no sense of hubris about the grand design or anything about it, or trying to impose a story or a tale on top of all this. It's looking at a game in its fundamental sense of what you're doing has to be fun. It's not a matter of beating the game into submission or accomplishing something, the actions have to be fun. There has to be something that you wanna just go out and do. People don't play softball because they want to beat the game of softball; it has to be an action that's fun by itself. I think that we succeeded in a lot of ways there.

Unlike many people in the games industry, I have absolutely zero desire to be making movies that go on the computer. And that's the downfall of a lot of companies. A lot of game designers wish they were directors, but I think you should make up your mind. And I'm clearly in the game designer part, rather than the director part."

Carmack was inducted into the Academy of Interactive Arts and Sciences' Hall of Fame in 2001, and, as a founder of id Software, was presented with two Emmy Awards in 2007. In addition to his work as a game designer, Carmack is also the founder and lead engineer of Armadillo Aerospace.

In the movie adaption of Doom, released in 2005, the names of the fictional scientists Dr. Todd Carmack and Dr. Willits are references to Todd Hollenshead, John Carmack and Tim Willits, co-owners of id Software, and developers of the Doom franchise.