Sonic's World

Sonic's world (ソニックの世界), is the main planet and overall setting in the Sonic the Hedgehog series. The planet is usually unnamed except in other media, in which most early continuities instead took place on the fictional planet "Mobius". With few exceptions, the planet's name in the games was never mentioned; however, games were generally assumed to take place on an Earth-like planet, with some locations based on real-world places.

Concept
Sonic the Hedgehog was created as a mascot for Sega, replacing its former mascot Alex Kidd. In order to maximize the appeal of the new character, his background (and the planet on which he lived) was given no detailed information in any of the initial games of the series (from the first game through to Sonic R). This allowed the separate branches of the company (Sega of Japan, Sega of America and Sega of Europe) to each create its own stories to fit third-party sponsors such as comics and TV series.

The name Mobius was adopted by western cartoons and comics. However, since the release of Sonic Adventure, the term began to diminish in the context of the games. The name "Mobius" is sometimes believed to have originated from a mistranslation of a 1992 Yuji Naka interview, but Sega of America had been using the name since at least 1991.