Diablo is an action role-playing hack and slash dungeon crawler video game series developed by Blizzard Entertainment (and Blizzard North). As of May 30, 2012, the series has sold over 24.8 million copies worldwide. The series is made up of three core games: Diablo, Diablo II, and Diablo III. All three games are action role-playing and hack and slash games. Expansion games include the third-party published Diablo: Hellfire, which follows the first game, Lord of Destruction, published by Blizzard and released after the second game, and the recently released Reaper of Souls, which follows the third game. Additional content is provided through story elements explored in other media forms. The series is set in the fantasy world of Sanctuary. The three games in the series take place in similar geographic areas, with several common areas including the town of Tristram and the region around Mount Arreat. Additional setting is provided by the High Heavens and the Burning Hells, two separate realms with ties to Sanctuary. The series focuses on the battle between the humans living on Sanctuary and the Prime Evils, demons who are led by Diablo, the series’ chief antagonist. The humans are occasionally aided by angels, notably the archangel of justice, Tyrael. The characters in the world of Sanctuary are primarily humans, angels, and various classes of demons and monsters. The series has resulted in the publishing of several books relevant to the Diablo setting, covering a wide range of the timelines of the universe. There are also comics that explore various stories within the world of Sanctuary.