The mainline games in the Sonic the Hedgehog series center around conflicts between the titular protagonist and namesake, Sonic the Hedgehog, and his arch-nemesis, Dr. Ivo Robotnik, better known as "Dr. Eggman". Sonic is the blue hedgehog noted for his carefree and cool attitude, capable of running at supersonic speeds and curling into a ball, allowing him to attack enemies.[2][3] Dr. Eggman is a human mad scientist and Sonic's nemesis with an IQ of 300 who seeks to conquer the world to establish a totalitarian regime called the "Eggman Empire" or "Eggmanland", where all nature is replaced with machines.[2][4][5] Being inspired by the culture of the 1990s, Sonic the Hedgehog runs on environmental themes, based on the then-growing debates between environmentalists and developers: Sonic represents "nature" and Eggman "machinery" and "development".[6]