Alfonso John Romero (born October 28, 1967 in Colorado Springs, Colorado) is a game designer, programmer, and developer in the video game industry. He is best known as a co-founder of id Software and was a designer for many of their personal computer games (all subsequently ported to consoles) including Wolfenstein 3D, Doom, and Quake. His game designs and development tools, along with new programming techniques created and implemented by id Software's lead programmer John Carmack, led to a mass-popularization of the first person shooter, or FPS, in the 1990s. He is also credited with coining the FPS multiplayer term "deathmatch".

John Romero's first game, Scout Search, was published in 1984 by inCider magazine, a popular Apple II magazine during the 1980s. Romero's first company, Capitol Ideas Software, was listed as the developer for at least 12 of his earliest published games. Romero captured the December cover of the Apple II magazine Nibble for three years in a row starting in 1987. He also won a programming contest in A+ magazine during its first year of publishing with his game Cavern Crusader.

Romero's first industry job was at Origin Systems in 1987 after programming games for 8 years. He worked on the Apple II to Commodore 64 port of 2400 A.D., which was eventually scrapped due to slow sales of the Apple II version. John then moved onto Space Rogue, a game by Paul Neurath. During this time, Romero was asked if he would be interested in joining Paul's soon-to-start company Blue Sky Productions, eventually renamed Looking Glass Technologies. Instead, Romero left Origin Systems to co-found a game company named Inside Out Software, where he ported Might & Magic II from the Apple II to the Commodore 64. He had almost finished the Commodore 64 to Apple II port of Tower Toppler, but Epyx unexpectedly cancelled all its ports industrywide due to their tremendous investment in the first round of games for the upcoming Atari Lynx.