Shadow the Hedgehog is a character shrouded in mystery and darkness. Referring to himself as "The Ultimate Lifeform", he is one of the three playable characters in the dark side story of Sonic Adventure 2: Battle, and while some of his backstory is revealed and hinted at in the game, the entirety of it is quite fascinating.

Shadow was created by Professor Gerald Robotnik using DNA from a creature called Black Doom. The purpose of his creation was to help provide a way to cure Gerald's granddaughter, Maria, who had an illness with no known cure. Shadow bonded with Maria as they lived together on the Space Colony ARK. Eventually Shadow was put into stasis by G.U.N. for fear that he was too powerful.

It would not be for another 50 years that Shadow would wake again. At this time Dr. Eggman (Professor Gerald's grandson) broke into ARK and released him. Eggman manipulated Shadow into joining his plans for world domination, but eventually Shadow remembered his promise to Maria to protect humanity.

Shadow's story in Sonic Adventure 2 culminates in over-exerting himself to help stop the end of the world and, in the end, as far as the other characters know, dying. It would not be until later games that it would be revealed what happened to Shadow: he survived, but lost all memories of his past.