The Evangelion, or EVA unit from Neon Genesis Evangelion is a biological creature designed to combat the angels and instigate Third Impact.

The EVAs are clones of the first angel Adam, or, in the case of EVA-01, Lillith. They have metal restraints to help keep them under control. They also contain a human soul trapped within, lying dormant (they have no soul of their own and the presence is needed for the AT Field).

The main defence is the AT Field, the barrier of the soul. In combat the EVA's AT Field will corrode the angel's, leaving it vulnerable to the more recognisable forms of weaponry such as the progressive knife or the pallet gun.

Only children conceived around the time of Second Impact are able to pilot the EVAs. Piloting is done via a direct neural connection, not only do the pilots' thoughts become actions, but injuries to the EVA result in pain for the pilot.

The first productions of EVAs lack an S2 engine so their enormous energy requirements are met by drawing power from a large umbilical cable. When this is cut, backup power lasts between 1 and 5 minutes of normal usage, although when put under minimal power it can last for many hours.

The power may in fact be for the restraints (with a fail safe keeping it inactive without the power) based on the EVA's ability to berserk, the soul within the EVA will awaken and take control, berserkers are often extremely brutal, have a lot of control over their AT Field and do not require energy from the umbilical or internal batteries.

The mass produced EVAs have an S2 engine so require no separate energy source.

With their ability to create an AT Field they remain the only weapons able to defeat the angels, however their main purpose is to instigate Third Impact. The exact details of how they would achieve this is dependant on whose plan of action is decided upon.

Another purpose, one that Yui Ikari believed, was that EVA was created so that humanity would survive, even after the end of our universe, EVA-01 would still around as a testament to our existence.