The Eggman Empire is a technocratic dictatorship founded and ruled by scientific genius Dr. Ivo Robotnik (aka Dr. Eggman). At least, that is the doctor's dream. Throughout the Sonic the Hedgehog video game series, Eggman's ultimate desire is to rule the world and make it a utopia for the scientific elite and robotic beings, where he will be acknowledged by all as the greatest scientific mind to have ever lived. As yet, his goal of world domination has not been achieved, with his so-called "empire" being nothing more than himself and his army of Badniks operating out of whatever bases the doctor has established. Eggman refuses to give up his quest no matter how many times Sonic has defeated him, and while society has labeled him a lunatic and a terrorist, he will always see himself as a genius and a king.
Dr. Eggman has come close to founding the Eggman Empire in three of the Sonic games.
In Sonic CD, Eggman invades the tiny world known as the Little Planet, which appears in orbit once a year. He anchors the Little Planet to Mobius with a giant chain and transports his Badniks there to mechanize the whole planet, turning it into an ugly ball of machinery. Because of the presence of the seven Time Stones on the Little Planet, the timestream is in flux and so Sonic the Hedgehog is able to pass through different time periods: from the unspoilt past to the post-apocalyptic future. In the game's "bad future" stages, the mechanized landscape has been heavily damaged due to Eggman's negligence and his robots have all fallen into disrepair. This gives a clear indication that Eggman would not make a good Head of State and his conquest is doomed to failure even if he wins.
In many of the Sonic games, Dr. Eggman has stated that the capital of his empire will be known as Eggmanland, and he has tried to build this city many times. In Sonic Unleashed, he succeeds in creating Eggmanland using a construction system powered by the energies of a monster called Dark Gaia, which he awoke from within the planet by shattering the world to pieces. The city he established looks more like a mish-mash of factories and carnivals, with industrial complexes and amusement park rides everywhere within the city's walls. Thanks to Sonic the Hedgehog and Light Gaia (also known as Chip), Eggmanland was destroyed after being pulled beneath the planet's crust and into its molten core.
Sonic Chronicles: The Dark Brotherhood
In this handheld Sonic RPG, Dr. Eggman helps Sonic and his friends to try and stop the Nocturnus Clan from stealing the Chaos Emeralds. As the Nocturnus Marauders retreat to their base in the Twilight Cage - a dimension where time moves much slower than on Sonic's world - Eggman and Tails build a spaceship that will allow the heroes to follow them. Eggman stays behind while Sonic and friends travel into the Twilight Cage. When the heroes return, they find that two years have passed in the few hours that they were in the Twilight Cage. During that time, Dr. Eggman conquered the world without Sonic around to stop him.
No direct sequel to The Dark Brotherhood has been made, so the story has been left on a cliffhanger. It is unknown if the story will ever be resolved.
In the Sonic Archie universe, Robotnik Prime conquered Mobius after launching a coup against the Kingdom of Acorn and rebuilding the city of Mobotropolis into Robotropolis. For over ten years, Robotnik terrorized the planet with his SWATbot armies, polluted the environment with his machines and roboticized most of the population. The only real opposition to his rule was Sonic the Hedgehog and the Knothole Freedom Fighters, who finally achieved victory over the tyrant after a decade of guerilla warfare. The peace that followed was short-lived, however, as Robotnik would soon be replaced by an alternate universe version of himself: Dr. Eggman. Since arriving on Mobius Prime, Eggman has established the Eggman Empire as the planet's ruling body. He has built new robots to replace the outdated creations of his predecessor, has recruited the group of techno-fanatics known as the Dark Legion and has even managed to destroy Sonic's original home base. Early on in his rule, Eggman's Roboticizer technology was rendered useless thanks to the alien Bem, who used their power to blanket Mobius in an energy field that de-roboticized its Robian population. The field has remained in effect and thus Eggman has been unable to re-roboticize any citizens living under his flag. He has since relied on forced slave labour and constructed robots to do his bidding, though he even lost most of these resources during the Enerjak crisis, which saw the destruction of his Badnik armies and his Egg Fleet, as well as leaving his capital of New Megaopolis in ruins. After several setbacks and a lengthy psychotic episode, Dr. Eggman has slowly but surely been rebuilding his fractured empire. He has built a new Death Egg superweapon and has even found a way to counter the Bem's de-roboticization effect.
Following the Worlds Collide crossover event, the world has been radically altered as Eggman interrupted Super Sonic's attempt to repair their fractured reality. Currently, the Eggman Empire remains as the strongest imperial body on the planet (which is no longer called Mobius or any other name), but the planet has been shattered into multiple fragments. The fragmented continents remain in close proximity to each other due to the presence of an entity known as Dark Gaia, a monstrous being that Eggman is now seeking to take control of. The full extent of Eggman's territories in this re-written timeline is currently unknown; the Death Egg remains as Eggman's primary base of operations and he controls such areas as Metropolis Zone and Bullet Station. Each of Eggman's territories are governed by an Egg Boss who commands a local branch of the Egg Army which consists of cybernetically modified Egg Soldiers and various Badniks.