Mephiles the Dark is the malevolent conscience, will and mind of the sun god Solaris. Although he was sealed in the Scepter of Darkness by Shadow the Hedgehog, he was released ten years later.

Full History.

Notes: The idea of Mephiles being sealed in the scepter and forgotten (Shadow Generations) is canon to this portrayal. His main verse is him attemping to claw his way back into the timeline. Up to your muse (if canon) whether they can remember him or not.