Shadow The Hedgehog

Shadow The Hedgehog is an artificial hedgehog, who is among the most popular characters in not only the series but in the franchise, too.

Biography
Shadow The Hedgehog was made in the 1950s originally designed by Gerald Robotnik to cure Neuro Immuno Deficiency Syndrome, a fictional disease that presumably affects the brain and immune systems. However, GUN agents arrived on ARK, where "The Ultimate Lifeform" was under construction. They seized the base and closed it for good. Shadow runs away with Mari Robotnik, his closest friend. Maria pushes him to an escape pod which sends him back to Mobius, but Maria was shot dead by the agents, and Gerald was seemingly killed too.

Shadow is strikingly very similar to Sonic in many ways, being a hedgehog and almost like his brother. In the ending events of Sonic Adventure 2, Shadow "dies" after he transforms back into his normal state, and plummets back to Mobius. Sonic and his friends say their last goodbyes before escaping back to their planet.

Shadow reappears in Sonic Heroes and his self-titled game as a clone, with his memory in a fog. He attempts to regain it by obeying Black Doom as part of a shady mission. His actions nearly destroyed Mobius, Sonic, and Eggman. Shadow then destroys Black Doom's mobile planet as Super Shadow, saving Mobius from Black Arms, and thus ending the three-way war.

Trivia
In the early development of SA2, Shadow was originally supposed to be named "Terios" which is Latin for "look-alike".