Tabris

The 17th angel, Tabris, is the "angel of free will". He appears in human form as Nagisa Kaworu, the fifth Children. Kaworu's origin is a mystery, his past is erased, just like Rei's, he also has similar features like the red eyes.
He is able to immediately synchronize at any desired level with EVA-02, which is especially astonishing as Unit-02 is not compatible with anyone aside Asuka. He soon get's familiar with Shinji, making him put trust in Kaworu, opening his heart. That makes it even worse for Shinji that he's finally betrayed by his new "friend", when Tabris manages to enter Central Dogma, acompanied by Unit-02, whom he commands from outside !
If in fact Adam were impaled in Central Dogma and not Lilith, the contact with Tabris would have "put a soul" into the giant creature, thus starting Third Impact. Tabris realizes his mistake (he calls Lilith an abomination), making it possible for Shinji in Unit-01 to defeat Unit-02 and capture Tabris in his hand.
Tabris/Kaworu then makes an astonishing statement. In his "becoming friend" to Shinji, he realized that though mankind was weak and quarrelsome, it posessed a divine gift, a free will (fruit of wisdom !), and that he found a precious soul in Shinji he couldn't waste.
So Tabris ask's Shinji to end his immortal existence in favour of a chance for mankind to survive. After a seemingly endless moment with Kaworu in Unit-01's hand, Shinji accomplishes his wish and squeezes his fist, killing whom he considered his only friend at that time. After that, he breaks down.