Biolizard

Biolizard is the prototype to the Ultimate Life Form. He was created by Gerald Robotnik to be an immortal creature, but instead Biolizard was locked away by G.U.N. He eventually was released, and it was revealed that Gerald had used him in a plan to destroy Earth. Sonic the Hedgehog and Shadow the Hedgehog eventually stopped Biolizard using the power of the Chaos Emeralds.