ANGELS:According to the Bible, Angels are the servants of God. In Neon Genesis Evangelion, angels are entities that appear in search of Adam, the first angel that appeared on earth. They are labeled as enemies of mankind. They are also powerful, sentient and capable to adapt to different situations.

"Humans found a god, and thus, tried to obtain it. As a result, humanity was punished. That was 15 years ago. The god that they found vanished. However, they tried to revive the god themselves. It was Adam. A human was made from Adam to be close to the god. That is Eva." - Ritsuko, Episode 23-"Tear" or "Rei III"
All of the angels, including humanity, the eighteenth angel, were born from Lilith.

"The other angels are just different possibilties of what we could have become." - Misato, Evangelion:Rebirth