Shadow the Hedgehog is a video game character from the Sonic the Hedgehog series. Despite looking like him, Shadow is not related to Sonic and was in fact, created 50 years prior the events of the main series.
Shadow was created aboard the Space Colony Ark by Professor Gerald Robotnik, as the world's Ultimate Life-form. A weapon for the military, and also as a cure for his sick granddaughter Maria.
Shadow made his first in-game appearance in Sonic Adventure 2 for the Dreamcast in 2001 and has gone on to star in several other games and media including Sonic X, an anime loosely based upon the Sonic Adventure series.