Kaworu Nagisa is a character and anti-villain in Neon Genesis Evangelion as well as it's manga adaptation and its film series remake Rebuild of Evangelion. He is a mysterious young man whom appointed as the Fifth Children up until revealed as the Seventeenth (Thirteenth in manga and film series remake) and final Angel called Tabris.
However, given to nature on how he came to being was almost in the same way with Rei, Kaworu is in fact, not just final Angel, but also the first Angel, Adam.
Neon Genesis Evangelion
Kaworu appears for a very short time in the original series. In episode 24, he appears sent by SEELE to begin the Human Instrumentality Project while posing as the Fifth Child and replacement for Asuka Langely Soryu. His goal is to make it to Terminal Dogma, where he believes Adam is held, and unite with his to begin Instrumentality. Along the way he meets Shinji Ikari and the two become quick friends. The higher ups at NERV quickly become suspicious of Kaworu based on how high his synchronization rates with the EVA unit were right off the start and they quickly suspect him to be the final Angel. Their suspicions are confirmed when Kaworu, revealed to be the Angel Tabris, takes EVA-Unit 02 and uses it to force his way past NERV's defenses and into Terminal Dogma. Shinji Ikari is called to stop Kaworu, but initially refuses to believe his friend is an Angel. He comes to the realization and gives chase in Unit 01. He is unsuccessful in stopping him and Kaworu reaches Terminal Dogma but is shocked to find the being there is not Adam, but rather Lilith. Kaworu believes that this destroys his purpose in life and begs Shinji to kill him, which he does after a long moment of hesitation. Kaworu's death sets of the events in End of Evangelion.
In End of Evangelion, the giant hybrid of Ayanami Rei and the Angels Adam and Lilith take his form for a short time in order to calm Shinji Ikari.
Neon Genesis Evangelion manga
Back when he was an Angel named Adam, Kaworu had distinct physical features that are never clearly shown, since, in the available glimpses of Adam's adult form, it is either partially covered by ice or in the form of a glowing silhouette, the "Giant of Light". However, he is visibly a giant humanoid with a morphology strikingly similar to that of an Evangelion, which is appropriate considering the genetic relationship between him and the Evas. As Giant of Light, Kaworu had a pair of shoulder pylons that implied to (similarly to what would be done with the Evas later) be added as restraint mechanisms by the research team whom found them, as a still-shot of the Katsuragi Expedition excavating Adam shows that the pylons were not initially present.
When initiating Second Impact, Adam revealed to possesses the ability to manifest translucent "wings" ("Wings of Light"), which it begins to spread before reaching the surface of the research base before greatly enlarge and split into four moments before it explodes. After Second Impact, his body reduced into an embryonic state resembling a tetrapod embryo (complete with four defined limbs) in early development.
When reborn as Tabris as result of Contact Experiment that caused the Second Impact in the first place by SEELE, Adam had his soul salvaged from his original body that reduced into embryonic state and emerged with human body. As human, he had pale white hair and skin as well as red eyes similar with Rei's. Even like Rei, he also gave off eerie atmosphere surrounding him due to his nature.
Unlike Rei, a being like him that mostly emotionless and less comfortable in her nature and identity, Kaworu is more comfortable with his true nature as Adam as well as warmer and more emotionally open. However he does show a detachment from human protocols and shares Rei's tendency to speak in universal rather than personal terms. Though he seems to have been sent to destroy it, Kaworu shows a marked interest in human culture, as well as human issues of pain and loneliness.
In manga, his personality is more or less same, but portrayed as being ignorant of human emotions and taboos regarding social interaction and personal space, creating some comic relief. The already eerie aura that he have even worse than in anime series due to him calmly killed a starved kitten whom followed Shinji.