Ring

Golden rings that are neccesary for Sonic to become Super Sonic. They also serve the purpose of being a sort of a life-meter. If you get hit by an enemy, and have some rings, you lose them all (unless you have a shield, which is lost instead of rings if you have it). If you get hit without any rings, you die.

Originally Sonic received an extra life for getting 100 Rings, and another extra life for 200 Rings. In later games, extra lives are also awarded at 300, 400, and further multiples.