The series takes place on Mobius, a planet mostly populated by anthropomorphic animals. The Kingdom of Acorn, based within the city of Mobotropolis, was at war with an unseen enemy. The King recruited a human scientist, Julian, to build war machines to end the war with a victory. However, during peacetime, Julian and his nephew Snively launched a coup d'état against the kingdom. The King is banished to another dimension, the Void, and the citizens are captured and transformed into robot slaves, through a machine called the Roboticizer. Julian renames himself as Dr. Robotnik, now the ruthless dictator of Mobius. Mobotropolis is renamed Robotropolis, a polluted, industrial cityscape.