Toby Fox

Fox has chronic wrist and hand pain that can regularly prevent him from programming and composing. He often uses speech-to-text software as a computer input method.

He cited a flare-up of this pain as one factor in the delayed development of the second chapter of Deltarune.

Fox began making role-playing games with RPG Maker and creating ROM hacks while he was in high school. His early projects included EarthBound Halloween Hack, also known as Press the B Button, Stupid!, which he submitted to the EarthBound fan site STARMEN.NET's 2008 Halloween Funfest. He used the alias Radiation while participating in the site's PK Hack forum.

Fox became interested in composing after discovering the music of Andrew Hussie's webcomic Homestuck. He joined the webcomic's music team, later becoming its leader and organizing musicians while editing tracks to fit the comic's scenes. His work included a version of "Megalovania" and gave him experience with digital audio workstations.

Fox developed a professional association with Hussie during this period. Part of Undertale was developed in Hussie's basement, and Fox first contacted artist Temmie Chang through her Homestuck fan art.

Fox began programming Undertale in January 2013 while he was studying at Northeastern University. He used GameMaker 8 as the game engine, FL Studio for music, and Microsoft Paint for sprite design. The game was developed over 32 months, with Fox handling nearly all of the development apart from its art assets. He recruited Temmie Chang to work on the art.

Undertale was released in 2015 as Fox's first major game outside ROM hacking. Its development was funded through a Kickstarter campaign, and the finished role-playing game sold more than 3.5 million copies. It became a breakout hit and received nominations for a British Academy Game Award, three Game Awards, and three D.I.C.E. Awards.

Fox conceived many of the game's characters, including Sans, Papyrus, Toriel, Asgore, Undyne, Mettaton, and the Annoying Dog. The Annoying Dog also became Fox's recurring avatar in games and online.

Fox released the first chapter of Deltarune for free in 2018. The game is set in a parallel universe to Undertale, and Fox developed it as a separate project rather than a direct sequel. He has described the original idea for the game as originating in a fever dream in 2011.

The second chapter was released for free in 2021. Fox later released Chapters 3 and 4 together, with the remaining chapters planned as additions to the same game. He has said that Deltarune is planned to contain seven chapters.

Alongside his own games, Fox composed music for Hiveswap, Escaped Chasm, Little Town Hero, Pokémon Sword and Shield, and Pokémon Scarlet and Violet. He also contributed music to Super Smash Bros. Ultimate, including a new arrangement of "Megalovania" for the game's Sans downloadable costume.

Fox has composed or contributed music for projects including YIIK: A Postmodern RPG, Omori, Touhou Danmaku Kagura Phantasia Lost, Fields of Mistria, and the Hiveswap games. His collaborations include work with ZUN, Itoki Hana, Camellia, and other musicians.

He made his voice-acting debut as Jared in an episode of the animated series We Baby Bears. He later voiced John Egbert in the Homestuck animated pilot.

Fox has cited EarthBound, MOTHER 3, Final Fantasy VI, Secret of Mana, Super Mario RPG, the Touhou Project series, Shin Megami Tensei, and the Ace Attorney series as influences. He has particularly highlighted the influence of Yoko Shimomura's music and the way Japanese role-playing games use characterization, battle systems, and recurring musical motifs.