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, ray casting for Hovertank 3D, Catacomb 3-D, and Wolfenstein 3D, 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. Quake 3 popularized the fast inverse square root algorithm. 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. In 2007, when Carmack was on vacation with his wife, he ended up playing some games on his cellphone, and decided he was going to make a "good" mobile game. 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 that id's parent company ZeniMax Media did not 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 to him from their purchase of id Software. In October 2018, Carmack stated that he and ZeniMax had reached an agreement and that "Zenimax has fully satisfied their obligations to me", ending the suit. On November 13, 2019, Carmack stepped down from the Oculus CTO role to become a "Consulting CTO" in order to allocate more time to his work on artificial general intelligence (AGI). On August 19, 2022, Carmack announced that he has raised $20M for Keen Technologies, his new AGI company. On December 16, 2022, Carmack left Oculus to focus on Keen. Workstyle Carmack has maintained a sixty-hour work week, working a 10-hour day, six days a week, throughout his career. He has spoken publicly about the importance of long hours of uninterrupted