Sonic the Clone (StC)

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 by Robotnik's latest weapon (a large drill), then him remaining in prison for several years until he finally managed to escape. The clone, convinced that he had come to the past by unknown means (his closest theory being that he ran so fast after escaping that he broke the time barrier), 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, convinced that he would never have recklessly put his friends in danger the way Old Sonic had, 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. However, once Robotnik had the Freedom Fighters in his custody, he gleefully revealed the truth that Old Sonic was a clone and not from the future at all. Old Sonic was horrified to learn that he was merely a copy. Using Sonic's super-speed, he managed to escape and find the real Sonic. Old Sonic revealed the whole story, and together they returned to rescue the other Freedom Fighters. While Sonic freed his friends, Old Sonic took on Robotnik in his battle-craft. Old Sonic trapped Robotnik in a cocoon of speed, nearly ripping apart the battle-craft. However, the extensive use of his super speed accelerated Old Sonic's already rapid aging, and he soon collapsed from exhaustion. Sonic was willing to find him help, forgiving him for his earlier trickery because he'd pulled through when the others needed him, but it was too late. Old Sonic's body finally wore out and he died, then transformed into pure energy and rose up towards the stars.