Lilim

The 18th and last angel, Lilim. Unlike the other angels, this is not a single being, but mankind as an entity. While the angels were in posession of the fruit of life, mankind ate from the fruit of wisdom, and while the angels were strong, single entities with supreme fighting skills, man is small and weak, and they don't like each other either.
In the process of the Human Instrumentality Project, Lilim had to be killed as well, so that "mother nature" (Lilith) would be able to collect all human souls and form a big, happy ghost entity without barriers, no AT-field hurting each other ... a somehow joyful as well as gruesome thought.
The light-creature seen on the picture is Lilith/Rei, standing on a field of crosses (each marking a dead human) at the End of Evangelion.