In December 2012, a self-taught musician with no formal programming background sat up late reading a Wikipedia article about array data structures. A few years later, a copy of the game that sprang from that page was handed to Pope Francis at the Vatican. This deep dive tells the story of Toby Fox and Undertale, from RPG Maker 2000 tinkering and Earthbound ROM hacks to composing for Homestuck, a $5,000 Kickstarter that raised over $51,000, and a September 2015 release that became a cultural phenomenon.

We explore how Fox avoided feature creep by making his code and narrative inseparable, why he built a game where you could talk your way out of every fight, and how rewriting the Toriel encounter so players could spare her became the moment he discovered what his game was about. We also cover his music-first development process in FL Studio, the deliberately simple art with Temmie Chang, the Papyrus rewrite prompted by a crying playtester, the toxic side of the fandom that drove Markiplier from his playthrough, and the quieter, episodic approach Fox has taken with Deltarune.

• How understanding arrays unlocked the typewriter text box that snowballed into a full battle system in Game Maker Studio
• The anti-RPG influences of Shin Megami Tensei and the 1997 game Moon, and Fox’s frustration with grinding and fetch quests
• Why composing the music before writing code dictated the pacing of dialogue and punchlines
• The genocide route, fandom policing of the correct way to play, and Fox’s admission he may never make something this successful again
• MatPat’s Jubilee of Mercy gift to the Pope, a Vatican jazz band playing a boss theme, and a multi-year orchestral tour launching in 2026