Satisfied that the small world had been ordered and that their work was done, the Titans prepared to leave Azeroth. However, before they departed, they charged the greatest species of the world, the Dragonflights, with the task of watching over Kalimdor, lest any force should threaten its perfect tranquility. There were many Dragonflights in that age, yet there were five flights that held dominion over their brethren. It was these five flights that the Titans chose to shepherd the budding world. The greatest members of the Pantheon imbued a portion of their power upon each of the flights' leaders. These majestic dragons (as listed below) became known as the Great Aspects, or the Dragon Aspects.
Aman'Thul, the Highfather of the Pantheon, bestowed a portion of his cosmic power upon the massive bronze dragon, Nozdormu. The Highfather empowered Nozdormu to guard time itself and police the ever-spinning pathways of fate and destiny. The stoic, honorable Nozdormu became known as the Timeless One.
Eonar, the Titan patron of all life, gave a portion of her power to the red leviathan, Alexstrasza. Ever after, Alexstrasza would be known as the Life-Binder, and she would work to safeguard all living creatures within the world. Due to her supreme wisdom and limitless compassion for all living things, Alexstrasza was crowned the Dragonqueen and given dominion over her kind.
Eonar also blessed Alexstrasza's younger sister, the lithe green dragon Ysera, with a portion of nature's influence. Ysera fell into an eternal trance, bound to the waking Dream of Creation. Known as the Dreamer, she would watch over the growing wilds of the world from her verdant realm, theEmerald Dream.
Norgannon, the Titan lore keeper and master-magician, granted the blue dragon, Malygos, a portion of his vast power. From then on, Malygos would be known as the Spell-Weaver, the guardian of magic and hidden arcanum.
Khaz'goroth, the Titan shaper and forger of the world, bestowed some of his vast power upon the mighty black wyrm, Neltharion. The great-hearted Neltharion, known afterwards as the Earth-Warder, was given dominion over the earth and the deep places of the world. He embodied the strength of the world and served as Alexstrasza's greatest supporter.
Thus empowered, the Five Aspects were charged with the world's defense in the Titans' absence. With the dragons prepared to safeguard their creation, the Titans left Azeroth behind forever. Unfortunately it was only a matter of time before Sargeras learned of the newborn world's existence....
World of Warcraft Community Site Chapter I: Mythos - Charge of the Dragonflights