A 4,000 year old weapon from the "4th great civilization", an ancient culture that was ultimately destroyed by the robot it created. Called a "Gizoid" (meaning "everything" in the ancient tongue), this robot was designed to record combat techniques and weapon data through observation. The Gizoid would accept orders only from the one who demonstrated the greatest power: a pact is known as the "contract". Eventually, the machine went out of control and decimated the civilization that created it.

4,000 years later, the dormant Gizoid was discovered by Pr. Gerald stuffed away in a warehouse. Gerald soon learned the robot's true nature, but found himself unable to dismantle the ancient technology. When affairs surrounding Project Shadow starting getting tense, the government demanded that the Gizoid be handed over. Though he knew the military would use the robot for its own gain, Gerald had little choice but to comply. Before handing the machine over, however, he reprogrammed its central computer with an emotion-based AI system that would allow it to make its own (hopefully virtuous) choices. Under the military's ward, the Gizoid quickly lost control after absorbing power from a Chaos Emerald, but GUN troops were able to deactivate the rampaging robot it and seal it away.

50 years later, the machine was discovered again by Dr. Eggman, who planned to use the device for his own conquest schemes. Frustrated over his inability to get the dormant Gizoid to work, however, the Doc dumped the contraption at Emerald Beach where it was subsequently re-re-re-discovered by Sonic. When Sonic and Tails learned that the robot evolved with Chaos Emerald power, Sonic nicknamed the contraption Emerl (short for Emerald). As Emerl evolved, it picked up personality traits from its 7 "masters" (Sonic and the others) and eventually turned into a fun-loving robot with a passion for sport fighting. Unfortunately, once it absorbed all 7 Emeralds, it went out of control and had to be destroyed by Sonic.