Mobius

Mobius is the planet that the Sonic the Hedgehog characters are from in SatAM, Adventures of Sonic the Hedgehog, Sonic Underground, and the comics. Mostly antropomorphs live there. Note that while originally, the American storyline also had Sonic games set on Mobius, the Japanese manuals have always had Sonic living on Earth, and since post-Sonic Adventure games have followed the Japanese storylines in all regions, it's safe to say Sonic has always lived on Earth in the games. Mobius is offically a present Earth, while in the comics, it is a future Earth.

Adventures of Sonic the Hedgehog
The animated series Adventures of Sonic the Hedgehog provided one of the earliest versions of the planet Mobius. The overall look of the planet was cartoony and the population ranged from the series standard humans and anthropomorphic animals to sausage people and other oddities.

In this continuity, as in the Japanese version, the place is completely free, with Dr. Ivo Robotnik just trying time and again to take it over (and usually failing miserably).

Sonic the Comic
Sonic the Comic, a UK-based comic published by Fleetway, and certain other books, provided a Mobius backdrop far more consistent with the style of the first few games. Once again, the inhabitants of the planet were anthropomorphic animals. Sonic the Comic notably divided the planet up into "zones", each with its own distinctive landscape and climate, in a similar manner to the early games. Key Zones were the Emerald Hill Zone, home of Sonic and a frequent target for Robotnik; the Metropolis Zone, here a capital city (with its skyline looking much like Mega-City One) for the planet and Robotnik's base of operations, via his Citadel Robotnik building; Casino Night Zone, given residential areas and the haunt of recurring gangster villain Max Gamble; Chemical Plant Zone, setting for the Tails 'Zonerunner' stories; and Mushroom Hill Zone, where the Emerald Hill folk hid to escape Robotnik. Original Zones, like Stone Tower and the upper-class El Dorado Zone, were also created,

In this version, Robotnik eventually took over the planet and ruled as dictator for years, using his subjects as slaves and forcibly turning them into Badniks. He was eventually overthrown and went into hiding, however. A recurring theme through the latter half of the comic's run was that there had once been a war on Mobius between an ancient echidna race (of which Knuckles is one of the last survivors) and the Drakon Empire. The Chaos Emeralds (important in this continuity, as in the games) were a product of that ancient war, and both the Aquatic Ruin Zone and Flickies' Island were old Drakon outposts.

In one issue of the comic, Amy Rose and her friend Tekno travelled to the dawn of life on Mobius, here shown to be caused by a team of scientific dinosaurs in spacesuits who worked for what was hinted to be God. Amy & Tekno also travelled to the planet Earth, and as a result of this story, rogue British military forces subsequently invaded Mobius before being hurled out by the spirit of the planet itself. A later story showed that, due to their highly similar ecosystems, Earth & Mobius were twin planets.

The subsequent fusing of the energies of Mobius with the enlarged sub-atomic world of Shanazar caused portals to open to various worlds and dimensions on Mobius, including various points in time in Earth's history. The comic ceased its run after adapting Sonic Adventure, though judging by the way they dealt with the events of that game, it is unlikely the writers would have done anything to change this view of the planet.

SatAM and Archie continuities
Although it was never mentioned in the SatAM show itself, Season 2 head writer Ben Hurst mentioned that he had intended for later seasons to establish Mobius as a future Earth but the series was canceled before such plans would be solidified. The society of SatAM's Mobius consists of anthropomorphic animals called Mobians, ruled by a dictator known as Dr. Robotnik (formerly called Julian) who aims to replace Mobian life with robots via roboticization.

In the Archie Comics version of Sonic, the writers eventually revealed a similar "future Earth" idea themselves, presumably as a result of the Sega of Japans' decision to do away with Mobius and present it as Earth. Mobians were revealed to be by-products of a genetic bomb dropped many millennia ago by an alien race known as the Xorda. This bomb apparently caused some animals to incorporate a great amount of human DNA. The same bomb also created Overlanders (see below). Contrary to this "Mobius-is-Earth" retcon, earlier comics had stated that Mobius exists in an entirely different universe from our own that can be reached through the Cosmic Interstate, an intergalactic road that connects different universes and realities across time and space. A possible way to rationalize this is to state that the time between the various realities in Sonic is not always in sync. Though, the comics appear to conflict, between Mobius-is-earth or another dimension, you can combine both ideas into one. Mobius IS in another dimension and IS also a future Earth of this particular dimension. In this dimension, Earth had the aforementioned cataclysm and then evolved into Mobius.

Overlanders and humans in Archie
Attempting to reconcile the presence of the obviously human Dr. Robotnik with a planet occupied mostly by Mobians, the Archie writers created the concept of Overlanders, four-fingered humanoids in constant conflict with Mobians. The Overlanders and Mobians famously fought in a Great War, during which the traitor Ovi (see above) helped the Mobians and gained the king's trust. When Mobius was revealed to be Earth, the Overlanders were explained as descendants of human beings who evolved and overcame the Xorda's genetic bomb.

After their defeat in the Great War, a group of overlanders traveled to space seeking out a better life though their journey would eventually take them back to Mobius though not before having a chance encounter with the Xorda which would serve as the cause for the alien's return.

In addition to Overlanders, Mobius has a smaller population of somewhat friendlier humans, who are identical to modern-day human beings who do not share the feelings of racism towards Mobians that seem common to the Overlanders. They survived the Xorda bomb unharmed as they were on board a passenger jet in mid-flight during the attack and crash landed beside a giant mountainous cavern in which would eventually become the human built-city of Station Square. These humans were rediscovered during the time at which the comic's adaptation of Sonic Adventure takes place. Overlanders and humans, despite their minor differences, now occupy a common home in Station Square though as can be pointed out through several appearances in events that proceed the overlander retreat to space, it would appear that the presence of Overlanders on Mobius is not limited to just Station Square. the United Federation which Station square founded is currently allied with free Mobians to fight the Eggman Empire.

Sonic Underground
Like in SatAm, Mobius was conquered by Robotnik who polluted and Roboticised most of the planet. Unlike SatAm, most of the Mobian population remained alive (as only those breaking Robotnik's laws were Roboticised). Mobius possesses a large aristocracy, who - outside of taxes - are largely untouched by Robotnik's reign; the vast majority of the population are lower-classes who live in slums & squalor, fearful of being arrested at any time.

Mobian Chronology
This planet bases chronology on four different ages on people.

Physical/Physiological age
This age is based on how a person looks like.

Activity age
This is based on how many years a person has been active.

Existence age
This is the closest to chronological age, but chronological age is a person's real age, based on the amount of time that has gone by in that person's life. If someone is mortal, their existence age agrees with that. But with immortals, like Shadow, existence age shows how long a person has lived, but isn't their real age. An immortal's real age may be 75, but their existence age may be 100,000. Since technically immortals stop at an age, that's what Mobians take into account (Yuji Naka based Shadow's age by Mobian chronology).

True age
This is how old a person really is. For mortals, this is based upon existence age. It is not based on existence age for immortals(see above article).