Gift of demigod-status
Long ago, Aviana was a normal raven, until she was chosen by Elune to deliver messages from the moon goddess to the demigod Cenarius. Soon she was carrying messages among many of the powers of the ancient world; each power granted the raven new abilities required to carry out her duties until she eventually became an equal among them. ( )
Well of Eternity
As the Kaldorei gathered at the Well of Eternity, Aviana took the form of a night elf and joined their studies of magic. When Queen Azshara built her temple and gathered together her chosen servants to revel in their arcane power, Aviana realized the corrupting influence of magic and returned to Elune’s side. ( )
War of the Ancients
During the War of the Ancients, Aviana would occasionally take mortal form and guide groups of endangered humans or night elves away from the Doomguard. However, most of the time she flew high above the land gathering information for Cenarius on the movements of the Burning Legion. ( )
During this conflict Aviana was "killed" when a large group of demons attacked her. The Doomguard surrounded her and pierced her body with their spears. As the blood spilled from her dying body, the demons that came in contact with it became infested with its blessed powers and were purified. When Aviana died, her realm tree G'Hanir died with her.
However, apparently she had not be destroyed, and still acts as a messenger and spy for Elune.
Aviana is known to many races including trolls, elves, tauren, and dwarves, often taking the form of those races to spy from within. The native races of Azeroth depict Aviana differently. The night elves see her as an enormous raven, taller than even the tallest tauren, but other races see her as a dove or an eagle, and she loves all such forms. Yet each race also knows her as one of its own kind, combined with scores of faces and roles — from a human wanderer or a Quel’dorei sorcerer to a dwarven explorer or a troll priest. Even the night elves revere the Lady Raven as one who walked the path of magic yet was wise enough to turn away before being corrupted. Though she is the patron of those seeking knowledge, they understand that she carefully guards that which she knows lest she let slip the secrets of the gods themselves. Still, she has a fondness for mortals that leads her to protect and aid them whenever she feels able. ( )
In serving a wide array of masters, Aviana in turn developed a wide range of influence. Her primary role is that of messenger, carrying information from one god to another and, on occasion, from the gods to mortals. These messages, combined with her own studies and observations, have granted her an incredible wealth of knowledge that has also made her a patron of scholars. However, as she is reluctant to share her knowledge, those who pursue secrets and mysteries also follow her path. Her most ardent followers are those among the Druids of the Talon, who themselves transform into birds to gather battlefield intelligence and carry messages. ( )
She appears with a flutter of large wings, but nothing can be seen until a tall figure clad in black leather steps from the shadows. Perhaps it is her loose-fitting cloak or the shadows cast across her face by a broad-mouthed hood, that makes it difficult to make out her race. Yet it’s impossible to miss her sharp green eyes, peering out from the hood and cutting into the very center of a person's being. ( )
Aviana prefers to keep her distance from combat, acting primarily as an observer or messenger. When drawn into battle, she will strike from a distance for as long as possible using her magic and her longbow before changing into raven form to charge and claw opponents while trying to make her way to freedom.
In the War of the Ancients Trilogy by writer Richard A. Knaak, it is hinted that some Night Elves were altered and became forest guardians. So some fans speculate, that these Night Elves may be the Harpys. The death of Aviana during the War would have left them without their matriarch, and could explain their now brutal nature (although Aviana herself also hinted to having these streaks).