E-100 Alpha - more commonly known as ZERO - is the first of Dr. Eggman's E-100 models and a prominent threat in Amy Rose's story in Sonic Adventure. This robot has a distinct bucket shape and shows little resemblence to the succeeding E-100's. It has no legs, instead travelling via hover-jets built into the lower portion of its body. It is heavily armoured and there are few attacks than can actually damage it, any attack made against it only aggravating it. Throughout Sonic Adventure, ZERO relentlessly pursues Amy Rose and a small Flicky bird which carries a Chaos Emerald. It uses a sensor beam emitted from its head to lock on to targets and then launches its hands to grab them. Its hands extend out on barbed metal cables that can be electrified and swung around to sweep away foes. It can also attack by pounding the ground and sending out a shockwave to knock enemies off their feet. As mentioned above, ZERO's armour cannot be damaged by most attacks, though it can be electrocuted, which will cause a hatch on its head to pop open and reveal its power cell. The power cell can be damaged and three blows from Amy's hammer is enough to destroy the robot.
Although ZERO was destroyed in Sonic Adventure, it would appear again in Sonic Advance 2 to chase Sonic through the special stages. It was referred to as Eggman's Guard Robot in that game.