Rhok'delar, Longbow of the Ancient Keepers

Rhok'delar, Longbow of the Ancient Keepers is the hunter quest bow. The quest involves defeating (solo, no pet or friends) four powerful demons and slaying the fearsome Onyxia.

Source
Rhok'delar, Longbow of the Ancient Keepers is created via the hunter epic quest.

Legend of the Longbow
The Ancients of Felwood were regarded by the night elves as the most powerful of their kind. When the Burning Legion invaded Kalimdor the first time, they corrupted the land. Felwood, once a lush valley of trees and beasts, became a scar on the land and a reminder of the corrupting powers the Legion possesses. The Ancients, too, fell prey to the corruption and have been locked in a petrified state ever since-but their spirits still linger.

Hunters who return with the of Vartrus the Ancient will be given a task to seek revenge against the agents of the Burning Legion who hide in the four corners of the world. Once their heads are returned as proof, the Ancients will help the hunter construct a bow, "The likes of which has not been seen in 10,000 years." The ancients will also create an, but downing the demons is not required for it.

Both Rhok'delar and its companion are living weapons. Rhok'delar is known to spontaneously sprout blossoms and Lok'delar glows with nature's aura, giving its owner innate resistances to poisons and nature-based spells.