E-102 Gamma is the second of Dr. Eggman's E-100 models and the first playable robot character to appear in the mainstream Sonic the Hedgehog games. Gamma's one and only canon appearance is in Sonic Adventure, his entire life spanning the course of the game's events.
E-102 was built within Dr. Eggman's Final Egg base and its frame contained a Flicky bird as an organic battery. Upon activation, Gamma was commanded by Eggman to engage in target practice and then to fight his older 'brother' E-101 Beta to earn a place on the Egg Carrier. Gamma succeeded in his trials and was assigned to Eggman's new battleship along with three succeeding E-100 units. Their first mission was to scour Station Square in order to find a mutant frog which had swallowed a Chaos Emerald and played a pivotal role in Eggman's latest scheme.
The E-100 units were dispatched and Gamma found Froggy in Emerald Coast. During the mission, Gamma found himself being transported to another place and time by the spirit of Tikal, and witnessed the echidna girl's first encounter with the creatures known as Chao. Such an encounter should not have mattered to Gamma, but left the robot filled with a sense of confusion. When Gamma returned to the Egg Carrier in his own time, he delivered Froggy to Dr. Eggman, who then punished the E-100 robots for their failure by banishing them from his ship. Eggman's careless disregard for his creations would further confound Gamma, who shortly after witnessed the chassis of E-101 being upgraded in the Carrier's workshop.
The confused robot was then ordered by Dr. Eggman to visit the ship's brig to retrieve a Flicky bird that had been locked up along with a girl. The girl - Amy Rose - refused to give the bird up. Gamma was curious as to why Amy would not surrender the bird and did not know why Eggman wanted it to begin with. Confused by Amy's refusal and the bird's recognition of him, Gamma's programming became corrupted by the will of the bird within its body. It decided to release Amy and warned her to get off the Egg Carrier before it reached Eggman's base. Shortly afterwards, Dr. Eggman commanded Gamma to report to the ship's outer deck to battle Sonic the Hedgehog, who had boarded the vessel to rescue Amy. Gamma fought against Sonic until Amy stepped in, urging them to stop. Soon, the Egg Carrier began to lose altitude and Amy's kindness towards Gamma wiped away the robot's lingering obligation towards Eggman. The robot fled the doomed ship, declaring Dr. Eggman as an enemy and the banished E-100 robots as friends that needed to be "rescued".
One by one, Gamma would track down the other E-100's and destroy them, releasing the animals trapped inside their bodies. His search would eventually lead him back to the downed Egg Carrier where he would battle E-101 Beta once again, who had been rebuilt and was considerably more powerful than before. Despite its new enhancements, Beta was still no match for Gamma and was defeated. Just as Gamma stood over his fallen brother ready to deal the final blow, Beta caught a second wind and blasted Gamma. Both robots had been badly damaged and they both exploded upon the Egg Carrier's deck, releasing the Flicky birds within each of them.
- Laser Targeting System - A sensorscope on Gamma's head allows him to tag multiple targets and automatically fire upon them in the order they are tagged.
- Laser Blaster - Gamma's right arm is equipped with a laser rifle which will automatically target and fire upon tagged enemies.
- Hover Mode - A fan emerges from inside Gamma's torso that allows him to hover above water and grants him limited flight ability.
- Jet Booster - A disc-shaped jet engine on Gamma's back allows him to fly and slow his descent.
- Wheel Mode - To cross terrain quicker, Gamma can kneel down and roll across the landscape on the wheels attached to his heels.