Sonic the Hedgehog (ソニック・ザ・ヘッジホッグ Sonikku za Hejjihoggu?), also referred to as Classic Sonic (クラシックソニック Kurashikku Sonikku?), is a character that appears in the Sonic the Hedgehog series. He is an anthropomorphic hedgehog and Sonic the Hedgehog's counterpart from another dimension set in the recent past. Well-known for his supersonic speed, iconic blue spikes and red shoes, Sonic has a huge fondness for freedom and adventures, and has spent a long time defeating the forces of his arch-enemy, the evil Dr. Eggman.[2]

Basically a past version of his modern counterpart from his younger days, Sonic first appeared during the Time Eater incident where he helped his counterpart foil one of Modern Eggman's plots before returning to his own universe. Since then, he has continued his adventures alongside his friends, and even reappeared in the mainstream universe to help out where needed.

More facts here: https://sonic.fandom.com/wiki/Sonic_the_Hedgehog_(Classic)