Early North American Canon

In 1991, during the production of the original Sonic the Hedgehog game, an internal document was written inside Sega of America to be used as a reference material for the plots found in early Sonic games (primarily in the instruction booklets as was usual in the '90s due to hardware limitations). This "Sonic Bible" was the basis for many iconic elements of early non-Japanese Sonic media, including the planet Mobius.

As a result of the Sonic Bible being used to present the story of many early Sonic games, the English versions of the games varied greatly from their Japanese counterparts until the late '90s. The release of Sonic Adventure on the Dreamcast saw a shift in Sonic games moving into fully-voiced cutscenes and longer and more detailed plots, effectively shelving the early canon from appearing in the games (though the concepts and characters established would continue to be used in other non-Japanese media).

Legacy
While the alternate stories and plot points have mostly been ignored in favor of the original story, various pieces of Sonic media has continued to reference parts of it.

Most notably is the inclusion of the name "Robotnik" in Sonic Adventure 2 as the surname of Gerald Robotnik, the grandfather of Dr. Eggman.