E-100,[4] codenamed α or Alpha (アルファ Arufa), or ZERO or Zero, and also known as the the Robot Guard (ガードロボ Gādorobo, lit. "Guard Robo"), is a character that appears in the Sonic the Hedgehog series. It was the prototype model for Dr. Eggman's E-100 Series, designating it as the zeroth E-100 unit, while E-101 Beta is designated as the first unit and E-102 Gamma is the second unit. During its last mission to recover one of the Chaos Emeralds, ZERO relentlessly pursued Amy Rose for the Emerald she unknowingly had until it had harassed her to the point of being on the receiving end of Amy's Piko Piko Hammer.