Symbolism

Evangelion :

The Evangelions are made by man as fighting machines to protect mankind against the angels. While Unit 01 is a direct clone of Lilith, all other Evangelions are siblings of Adam.
Now there are certain similarities between each Evangelion and the four Barons of Hell from Judeo-Christian mythology. This especially fits, as they were designed to fight angels and as well to fulfill the Human Instrumentality Project ... which would bring destruction to mankind
The first Baron has one large eye, that would fit to Eva Unit-00
The second Baron has a single horn upon its head ->Unit-01
The third Baron is blood red with four eyes and two jaws ->Unit-02
The fourth Baron is pitch black with exceedingly long arms ->Unit-03
Unfortunately, though this interpretation is quite fitting into the whole Bible/Qaballah setting of Neon Genesis Evangelion, it was explicitly contradicted by the makers of NGE, who explained that the EVA's were created after traditional Japanese demons. But the resemblance is striking, so let's pretend we didn't know :-)...