Tomb of Horrors is an adventure module written by Gary Gygax for the Dungeons & Dragons (D&D) role-playing game. It was originally written for and used at the 1975 Origins 1 convention. Gygax designed the adventure both to challenge the skill of expert players in his own campaign, and to test players who boasted of having mighty player characters able to best any challenge. The module, coded S1, was the first in the S-series, or special series of modules.