Shadow the Hedgehog

Shadow the Hedgehog (シャドウ・ザ・ヘッジホッグ, Shadō Za Hejjihoggu), also known as "The Ultimate Lifeform", is a character from the Sonic franchise. He first appeared in Sonic Adventure 2 for the Dreamcast console. Shadow was created by Professor Gerald Robotnik for the purpose of providing genes to cure the deathly ill, such as his granddaughter Maria. Shadow stayed at the Space Colony ARK, forming a close bond with Maria. Soon however, when the government had growing concerns over Gerald's work on immortality, the G.U.N invaded the ARK, killed Maria and locked away Shadow for fifty years before he was freed by Dr. Eggman.

Character Description
During the development of Sonic Adventure 2, it was decided that the motif of the game was to be between good and evil. To do this, the development team would create new characters designed to assist Dr. Eggman to combat the main protagonists of the Sonic series. Yuji Uekawa came up with a darker version of Sonic who was then dubbed "Terios" which means reflection of. During much of the development of Sonic Adventure 2, the Sonic Team did its best to keep Shadow's identity a secret in order to build up the hype for the game.

In Super Smash Flash
Shadow made an appearance in Super Smash Flash as an unlockable character. He was unlocked only after Sonic, Tails, and Knuckles have cleared Adventure Mode.