Toby Fox is an American developer and composer behind the 2015 hit indie video game Undertale.

In 2018, Toby Fox released Chapter 1 of his game Deltarune, following suit and composing the soundtrack on his own. Chapter 2 followed in 2021, Chapters 3 and 4 in 2025, and Chapter 5 in 2026, each accompanied by his music with minor contributions from other artists.

He has also contributed to other titles such as Homestuck, where he composed many tracks and albums under the name Toby "Radiation" Fox (and also voiced character "John Egbert" in it's animated pilot), Earthbound: Halloween Hack, the Hiveswap series, Pesterquest, Pokemon Sword and Shield, Pokemon Scarlet and Violet, Super Smash Bros Ultimate, Dweller's Empty Path and OMORI.

Fox is secretive and does not typically do interviews. He has chronic wrist and hand pain that regularly disables him from programming and composing. In September 2020, Fox cited a flare-up of this pain as a factor in the delayed development of Deltarune's second chapter.