Undertale is a role-playing video game created by indie developer Toby Fox. In the game, players control a human child who has fallen into the Underground, a large, secluded region underneath the surface of the Earth, separated by a magic barrier. The player meets various monsters during a quest to return to the surface, mainly through the combat system; the player navigates through mini-bullet hell attacks by the opponent cyclically, and can opt to spare monsters instead of attacking and killing them. These choices affect the game, with the dialogue, characters, and story changing based on outcomes.
Fox developed the entirety of the game independently, including writing and composing the score, with only additional art created by other artists. The game was inspired by the Mother and Mario & Luigi role-playing series, the bullet hell shooter series Touhou Project, and the British comedy show Mr. Bean. Undertale was initially meant to be two hours in length and was set to be released in mid-2014, but development was delayed over the course of the next three years.
The game was released for Microsoft Windows and OS X in September 2015, and later for Linux in July 2016. Upon release, the game was acclaimed for its writing, thematic material, intuitive combat system, musical score, and originality; with praise directed towards its story, dialogue, and characters. The game sold over a million copies, and was nominated for multiple accolades and awards, including Game of the Year from several gaming publications, winning others from conventions including South by Southwest.