When Sonic was only 5, the evil Dr. Robotnik took over the city of Mobotropolis. Due to Sir Charles' invention the roboticizer, Robotnik kidnapped Sonic's parents and roboticized them, leaving Charles to raise Sonic as if he were his own. Sonic grew up with his Uncle Chuck, and they developed a father-son relationship. When Uncle Chuck was roboticized, Sonic was devastated. He shortly formed the Junior Freedom Fighters (Junior because the originals were adult Mobians and roboticized).
Uncle Chuck the Spy
A long time after he was robotcized, Uncle Chuck gained control of his robot body, thanks to Sonic. He decided that instead of living in Knothole with Sonic and his friends, he would stay in Robotropolis as a spy. He would tell Sonic of any of Robotnik's plans, and help Sonic foil them occasionally.
When Sonic was flung into space, a mass deroboticization occured. Uncle Chuck was among the many who were deroboticized that day, along with Sonic's mom.
Sonic now lives with his parents and Uncle Chuck. Uncle Chuck and Sonic still hold a strong bond.