Not much is known about Sonic's early life. Although, he was born on Christmas Island and that he spent his life traveling around the world in search for an adventure.
At some point in his life, Sonic met Dr. Ivo Robotnik and they became enemies under unknown circumstances. After meeting each other, Sonic battled Robotnik in an untold number of confrontations as the mad scientist attempted time again to conquer the world, with Sonic each time emerging victories and foiling the doctor's plans. Despite their many battles, however, Sonic did not really account of his adversary.
South Island Battle
Sonic heard news about Robotnik and his robotic forces invading South Island after that the doctor discovered powerful relics, Chaos Emeralds, were hidden on the Island and sought them to use their power to produce weapons of mass destruction. Annoyed by Robotnik's perseverance, Sonic rushed to the Island to stop Robotnik. Once he arrived, he found out that Robotnik was enslaving the animal citizens there and forcing them to power his machines.
Despite being greatly outnumbered, Sonic saved the animals by destroying their robotic prisons and retrieve the powerful emeralds before Robotnik could get his hands on them. After eliminating robotic forces in different areas by saving his friends and securing the Chaos Emeralds, Sonic entered Robotnik's stronghold on the Island, defeated the villain and drove him off the Island. With Robotnik finally defeated, Sonic reunited with the animals at Green Hill Zone and then released the Chaos Emeralds; with their power ensured the Island's prosperity.
West Side Island Battle
Sonic traveled around the world in the Tornado in search for adventure, when he discovered West Side Island. Landing there and with nothing else to do, Sonic decided to relax and explore this new place. After a few days though, Sonic noticed someone was following him and found out it was a two-tailed fox cub named Miles "Tails" Prower, who had came to idolize him. At first, Sonic attempted to ignore him and leave him be. However, as Tails continued to follow him, Sonic was impressed that he could keep up, and decided to allow him to tag along, though he was still not particularly interested in him.
Later, during an early afternoon, Sonic was taking a nap under the Tornado until explosions awake him and find out Badniks were attacking West Side Island. Standing beside Tails during the initial attack, Sonic was angered when he knew Dr. Robotnik was behind this and ran running into the center of the attack to find the evil doctor.
Sonic fought Robotnik in his new inventions again, defeating him every time. After managing to free West Side Island, Sonic and Tails pursued Robotnik to the Wing Fortress Zone on board the Tornado. Afterwards, Tails helped Sonic up to the Death Egg and allowed Sonic to face Robotnik alone. Sonic managed to fight and destroy Robotnik's Silver Sonic and then chased Robotnik until the mad scientist deployed the Death Egg Robotnik. Through a long battle, Sonic defeated his machine and then sent the Death Egg to Earth, destroying it and defeating Robotnik once again.
Captured by Robotnik
Sonic was captured by Dr. Robotnik and imprisoned on Eggman Island where he was to be executed alongside Mighty the Armadillo and Ray the Flying Squirrel. Teaming with fellow prisoners, Sonic escaped his cell, only to blown at the other side of the Island with Mighty and Ray by a geyser triggered by Robotnik. The three prisoners infiltrated Robotnik's Tower and confronted their common foe but escaped when Robotnik triggered a self-destruction.
Later on, Sonic was travelling in Never Lake to travel to Little Planet, a small satellite that goes near Earth once a year, to explore it. When Sonic arrived, however, he found out that the planet was transformed into a mechanical wasteland and chained to a nearby Mountain, thus preventing it from leaving. After avoiding from falling mountain debris, Sonic noticed Robotnik's face carved into the mountain where the chain was embedded; immediately he knew that his arch-nemesis was behind this and up to no good again. On his way over, he met up with a pink hedgehog, Amy Rose, who was madly in love with him. Sonic therefore traveled to the Little Planet to liberate it from Robotnik's control. As he arrived, Sonic realized he could undo Robotnik's work by using the planet's time messages to change the past and collect the mystical Time Stones, Robotnik's reason for invasion on the planet. He saved Amy from his robot counterpart named, Metal Sonic, defeated Eggman, and escaped from Little planet from its collapsing control of Eggman.
Angel Island Battle
Sonic and Tails arrived at Angel Island, because Eggman invaded the island. Sonic in his super form, however, was ambushed by a Red Echidna, named Knuckles who stole the seven Chaos Emeralds from him. Meanwhile, when Sonic and Tails arrived at the Emerald Alter, Knuckles was tricked by Eggman because He's trying to steal the Master Emerald, which has special powers that neutralizes the energy of the Chaos Emeralds. Eventually, Knuckles befriended Sonic and Tails, and together they took back the Master Emerald, destroyed the Death Egg, took it back to Angel Island, where it belongs.