Demon's Souls is an action role-playing video game developed by FromSoftware, under supervision by SCE Japan Studio, for the PlayStation 3. It was published in Japan by Sony Computer Entertainment on February 5, 2009, in North America by Atlus on October 6, 2009, and in Australia and Europe by Namco Bandai Games in June 2010. It is the first installment in what became the Souls series of games.

Set in a dark fantasy world, players take control of a hero who has journeyed to the fictional kingdom of Boletaria, which is being ravaged by a cursed fog that brings forth demons who feast on the souls of mortals. The game has been described as a spiritual successor to the King's Field series of games. The gameplay involves a character-creation system and emphasizes gathering loot through combat with enemies in a non-linear series of varied locations. It has a unique online multiplayer system integrated into the single-player where players can leave useful messages and warnings for other players' single-player game worlds, as well as joining other players in their world to assist and/or kill them.

Upon its release, Demon's Souls was met with acclaim from critics, winning numerous awards. The game was praised for its dark fantasy art design, variation in combat choice and integrated online interactions. The game is particularly notable for its high difficulty level, with many critics noting it as a genuine challenge. The game Dark Souls, which itself spawned two sequels, is a spiritual successor to Demon's Souls, and was also one of the primary inspirations for Bloodborne.