E-101 Beta was an E-Series robot built by Dr. Eggman and the first of the E-100 models. Shortly after a practice mission, he was tasked with fighting the newly created E-102 Gamma to determine who would work on-board the Egg Carrier. Beta lost, but was kept around since Eggman 'could always use a spare set of parts.' Unbeknownst to Eggman, Beta set about remodelling himself. He was seen enacting this process by Gamma, who was searching for the captured Amy Rose and quickly put what he saw out of his mind. Beta and Gamma would not see each other again until Gamma visited the Egg Carrier's crash site. Beta, now fully reconfigured and flying, emerged to fight Gamma, a conflict which Gamma won. Just as Beta was finally brought down, he delivered one last shot to Gamma, fatally wounding him before exploding. His organic battery, a small grey Flicky hovered before the wounded Gamma for a moment, in search of its family before flying off, missing Gamma's self-destruction. A few seconds later, it swivelled around to find a pink Flicky heading towards it, the pair reunited at last.
Beta has also appeared in Sonic X, in a similar role to the one he played in Sonic Adventure, though in the anime he spoke a few times, acknowledging Gamma as his enemy and Eggman as his master. Also, both he and Gamma were not completely destroyed, both partially exploding, but their empty shells were seen to be holding hands as they burned following their last battle.