Good:

Sonic: A seventeen-year-old hedgehog who protects the planet from Dr. Eggman and other forms of evil.

Tails: A fourteen-year-old fox who is Sonic's best friend and sidekick.

Amy: Sonic's girlfriend and ally in fighting off evil with her hammer.

Shadow: Sonic's ally and a top agent for GUN. Serves as Silver's legal guardian.

Silver: A fourteen-year-old hedgehog that was rescued by Shadow and is his trainee.

Rouge: Shadow's partner and fiancé, who acts like an older sister to Silver.

Knuckles: Sonic's rival and friend, also the guardian of the Floating Isle.

Tikal: Knuckles' betrothed. His fellow guardian and healer after battles.

Queen Hope: Ruler of Crystalleen, and creator of the Amethysts. Has history with Lord Dominus.

Evil:

Lord Dominus: Ruler of The Dark Realm, and master to the Obsidians.

The Obsidians: Lord Dominus' soldiers that he sends out against the Amethysts.

Dr. Eggman: Enemy to Sonic and Co. In competition with Dominus for dibs on killing the Amethysts.