EVA-01 TEST TYPE. The first Eva to be introduced to actual combat, and the second Evangelion built at NERV HQ after Eva-00. Although it plays a major role in many battles against Angels, it also exhibits a number of unaccountable phenomena, such as going berserk, activating without an entry plug inserted, and remaining active after its operational time limit, etc. In the battle against the 14th Angel, it devoured the Angel and thus directly obtained an S² Engine.

Purple in colour, its dedicated pilot is the Third Children - Shinji Ikari. It seems that the soul of his mother - Yui Ikari -- was made to dwell inside Eva-01. Also, the physical body of Eva-01 was apparently created from Lilith. This is why when the Lance of Longinus was lost, Eva-01 became the sole substitute for Lilith as the medium for Instrumentality (Human Complementation).

Source: The End of Evangelion : Glossary contained within The End of Evangelion - Theatrical Program.