Shadow the Hedgehog is the end result of Project Shadow, a project to create the Ultimate Lifeform. Created by Professor Gerald in his efforts to find a cure to a rare disease known as NIDS that was affecting his granddaughter Maria, Shadow was gifted with the powers of the alien Black Doom through that entity's blood. After the project was forcibly shut down by the government, Shadow was put into stasis for 50 years and then awakened by Dr. Eggman, Gerald's grandson, to help him take over the world. Shadow sought instead to destroy the world to avenge Maria, who had been killed by the raid on Space Colony ARK where they had both lived. However, Sonic the Hedgehog and Rouge the Bat were able to convince Shadow that Maria would not have wanted such a result, and Shadow joined forces with Sonic to save the planet. Saved by aliens, he would return to join with Sonic and others against the evil Xorda. He would eventually rejoin Eggman, only to turn against him and join the special forces of the United Federation after learning the true purpose Gerald created him for.

Has a cannon voice. For reference, check here:

https://www.youtube.com/watch?v=366YWLLVHeo