Tabris
Tabris, unlike any of the other Angels, is human in appearance and hence is able to infiltrate NERV unnoticed which is vital as Tabris possesses little in the way of offensive capabilities.  Although Tabris's armament is limited, the Angel does, however, possess the ability to synchronise with an Evangelion both directly and remotely with ease, and at any desired synchronisation ratio provided that the Angel's soul is more dominant than that of the Eva's.  This ability allows Tabris to take control of the very same tool with which NERV intend to destroy the Angel. Besides this unique ability, Tabris is also capable of generating an exceptionally strong AT field.
Tabris' namesake was the angel of free will. Tabris took the form of Kaoru Nagisa, the fifth child. He appears only in episode 24, where he befriends Shinji. By that point, Shinji has been left pretty much alone. Asuka is catatonic and Rei is dead. Misato is begrieved with the loss of Kaji, who was a rascal and a scoundrel that she couldn't help but still be in love with anyway. All of Shinji's classmates have been evacuated away, with most of Tokyo-3's population. Shinji has been left alone as the sole remaining Eva pilot in defense against the anticipated last remaining angel. Enter Kaoru, introduced by Seele itself. Kaoru befriends Shinji, offering up various platitudes and expressing bewilderment at some of life's foibles. Then it turns out that Kaoru himself is the 17th angel, able to synchronize with an Eva without even being inside of it, as long as the Eva has no pilot. He sets Unit-02 in a struggle with Shinji in Unit-01, which wrecks some of the facilities of NERV. While this chaos goes on, Kaoru penetrates more deeply into NERV in the angels' search for Adam, than any other angel. What he finds instead, is Lilith, crucified to a wall. Finally Shinji defeats Unit-02, and grabs Kaoru. Strangely, Kaoru goads Shinji into killing him.