From Sonic - Wiki on Neoseeker

Eggman Nega as seen in Sonic Rush

[edit] History

Eggman Nega is Dr. Eggman's human dimensional counterpart. Eggman Nega made his first appearance in Sonic Rush. He has since been in other Sonic games, including Sonic Rush Adventure, Sonic Rivals and Sonic Rivals 2. He has been a main villain in every game he's appeared in so far and is even more evil than Eggman himself. He is the villain in Blaze the Cat's world. Eggman and Eggman Nega are from a different demension, and they are both trying to stop Sonic and Blaze the Cat so they can rule both of the worlds. he is a bit crazy to.