Robert F. "Toby" Fox (born October 11, 1991) is an American video game developer, composer, and voice actor. He is best known for developing the role-playing video games Undertale and Deltarune — both of which received critical acclaim. Undertale has received nominations for a British Academy Game Award, three Game Awards and D.I.C.E. Awards.

Fox's early work consisted of developing RPG Maker games and creating ROM hacks like the EarthBound Halloween Hack. Fox then moved on to composing music, most notably for Andrew Hussie's 2009 webcomic Homestuck.

Following the success of Undertale, he went on to compose music for a number of other indie games, as well contributing to the soundtracks of Super Smash Bros. Ultimate and the Pokémon video games.

Robert F. Fox was born on October 11, 1991, in Manchester, New Hampshire. Along with his three brothers, he is the son of Robert Fox, a financial planner, and Barbara Fox, a retired paraprofessional.^{[clarification needed]} Fox was raised as an Episcopalian. Fox has stated that as a child, he took music lessons, including piano and trumpet; when he reached middle school, he decided to start playing piano again, performing gaming soundtracks by ear. He later studied environmental science at Northeastern University and graduated in 2014.

Fox's earliest experiences in game development involved using RPG Maker 2000 with his three brothers to make role-playing games and creating ROM hacks in high school. His most notable early project was the EarthBound Halloween Hack, a Halloween-themed ROM hack of EarthBound, which released in 2008. He then moved on to compose a variety of music for Andrew Hussie's 2009 webcomic Homestuck during his senior year of high school. Though he did not initially respond when Hussie started a Music Contribution Team in April 2009 and put up a news post asking composers to participate, Hussie took note of his work when Fox started uploading piano covers of the webcomic's music on the MS Paint Adventures forums.

Fox was production coordinator of Homestuck's soundtrack until its conclusion in 2016, composing music including a version of "Megalovania"; he credited this with giving him experience with digital audio workstation software. Additionally, he has stated in a tribute post to musician George Buzinkai that tracks such as the unused Homestuck theme called "Patient" inspired Undertale themes such as "Another Medium". In particular, his remix of Buzinkai's song Doctor, titled "Savior of the Waking World", was a "turning point" in his musical journey; it was used as the background music for a major moment in the fifth act of Homestuck.

Fox's most well-known work is the 2015 role-playing video game Undertale, which he also composed the soundtrack for. The game sold more than 3.5 million copies, becoming a "breakout hit" and "pop-culture phenomenon". The game has received nominations for a British Academy Game Award, three Game Awards and D.I.C.E. Awards. Fox worked on the entire game independently, besides the art assets—which he asked Temmie (Tuyoki) Chang to help with—to avoid relying on others. He thought of the character designs and ideas for Undertale while in college, where he drew them in his notebook.

Following its release, Undertale garnered an extensive fanbase. Fox commented that he did not mind if people stated that they did not like the game, saying that it was "not for everyone". Despite Undertale's awards and widespread acclaim, in 2016, Fox wrote that his personal opinion was that the game was still "niche" and deserved an "8/10" review score.