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The Acheron Empire is a fictional historical kingdom found within the world of Robert E. Howard's Hyborian Age. It was first mentioned in the Conan the Barbarian novel The Hour of the Dragon as an ancient realm ruled by sorcerers and that collapsed before the timespan of the Conan stories. The name comes from Acheron, a river of the underworld in Greek mythology.
Acheron was first mentioned in Robert E. Howard's novel The Hour of the Dragon as an ancient empire in the history of the setting. It was not mentioned in his earlier essay "The Hyborian Age", which outlined the history of the setting, nor in any other of his works. Further works based on those of Howard expanded on the setting.
Acheron was a country that existed more than three thousand years before the time of Conan and the Hyborian Age. It occupied roughly the same area as the pseudo-European Hyborian nations of the Hyborian Age. Acheron was more advanced than their neighbors to the east and the west; it was equal to the contemporary empire of Stygia to the south and is described as never having been able to conquer the Cimmerians of the north. The wizards of Acheron practised dark magic such as necromancy. The empire was destroyed by the uprising of Hyborian barbarians, who had suffered under Acheron.
Roy Thomas used the fallen Acheron Empire from time to time in Marvel Comics publications. The Ultimates universe of Marvel Comics features an Acheron Empire, ruled by its version of Thanos and Ronan the Accuser
In the 2011 movie, Conan the Barbarian, Acheron is used a plot device in relation to the heroine Tamara who is a descendant of Acheron's necromancers.