Arcosin

Arcosin is a very rare Ancient of the Arcane, one of the few known in the Warcraft universe, and the only one that is friendly to players, albeit only to the Alliance. Arcosin is stationed at the Tower of Estulan, an outpost maintained by the Shen'dralar.

With the return of the Shen'dralar to the kaldorei, and being the only night elves who use arcane magic, perhaps the association is only a natural fit.

Trivia

 * His name is probably meant as a reference to the inverse trigonometric function arccosine (commonly read as cos^-1).