E-01 is the name of a very large, immobile, four-wheeled, cylindrical robotic unit that is the height of the central area of Death Chamber.
It is the gargantuan central core computer of Death Chamber in Sonic Adventure 2. Its "E-01" decal can be found near the top of its metallic outer shell. While some say it is an E-Series prototype, it seems more like a nuclear reactor and not much like a fighting machine. E-01 could potentially extend beyond Death Chamber.
It should be noted that the decal "E-01" appears throughout the Death Chamber above certain doorways. The reason for this is unknown.