Nearly all games in the Sonic the Hedgehog feature a blue anthropomorphic hedgehog named Sonic as the central player character and protagonist. The games feature Sonic's attempts to save his planet from various threats, primarily the evil genius named Dr. Eggman in Japan, and Dr. Ivo Robotnik in Western Regions, although he is usually named Dr. Eggman as of Sonic Adventure. The main antagonist throughout the series, Robotnik's aim is to rule the planet and establish the Eggman Empire or Eggmanland; to achieve this, he usually attempts to eliminate Sonic and acquire the powerful Chaos Emeralds.