Old Sonic

"Old Sonic" is an elderly blue hedgehog who claimed to be Sonic the Hedgehog from fifty years in the future. He looks, sounds and acts just like the much younger Sonic, although he has white whiskers on his chin and he wears half-moon spectacles and plaid slippers instead of sneakers.

Old Sonic claimed to have come from a dystopian future in which the Freedom Fighters had been killed and Robotnik's tyrannical rule over Mobius had become much worse. In fact, Old Sonic was a clone created by Doctor Ivo Robotnik from Sonic's DNA, as part of a scheme to defeat the Freedom Fighters. Old Sonic truly believed that he had time travelled from the future, but when he discovered the truth that he was not the real Sonic, he turned against Robotnik.

History
Doctor Robotnik took a cell sample from Sonic after capturing him, and (with some help from Grimer) used the cell sample to create a duplicate that he then grew in his laboratory. Robotnik intended to use the clone to attack and give Sonic a bad name, but something went wrong with the experiment and the clone aged too rapidly. Instead, Robotnik brainwashed the clone with a false memory so that he'd think he was from a future which "held no hope for outlaws". In particular, he was given a memory of his friends the Freedom Fighters being wiped out. The clone, convinced that he had come to the past by unknown means, believed that the only hope for peace was to follow Robotnik. He made a deal with Robotnik in which he would lead the Freedom Fighters into a trap, in exchange for Robotnik sparing their lives.

Old Sonic then sought out the Freedom Fighters, preventing Sonic from drowning in a swamp and telling them that he had come from the future to change history. Sonic himself was not convinced, even after a trusted doctor from the Chemical Plant Zone performed a DNA test that "confirmed" they were both Sonic. Old Sonic told the Freedom Fighters that his (Sonic's) reckless behaviour had resulted in the other Freedom Fighters being killed by a drill-shaped weapon in the Candlewick Green Zone. Sonic blamed himself for what happened, allowing himself to be taken to prison without resistance, while Robotnik turned Mobius into an even worse place. He claimed that, when he escaped many years later he ran faster than ever before, presumably leading him to "break the time barrier" and travel to the past. (It is not clear how much of this was part of the clone's false memory and how much was merely a ruse to lure the Freedom Fighters into Robotnik's trap.)

Sonic refused to believe it, but the other Freedom Fighters did and agreed to accompany Old Sonic on his mission to destroy the "Deadly Drill Machine" before it was even built. He led them to the caves beneath the Candlewick Green Zone, leading them into an ambush by Robotnik and his Troopers.

Trivia
Old Sonic was never given a specific designation. He was referred to only as "Sonic" or "the clone".