Elemental Sundering

The Elemental Sundering was a 5,000 year-long battle fought between the elemental forces of fire and air at the core of Azeroth.

The conflict was initiated by the Firelord, Ragnaros, who sought to expand his power by overcoming Prince Thunderaan, an elemental prince of wind. Ultimately, Ragnaros prevailed over the Prince of Air and fed on his essence as planned. The Firelord stored what remained of Thunderaan in the Bindings of the Windseeker.

Thunderaan would be successfully summoned on Azeroth from the bindings by mortals in a later age.

History
In the years preceding the arrival of the Old Gods on Azeroth and the subsequent rise of their Black Empire, the world was inhabited by the elemental lords. These powerful beings each represented one of the primal forces of the world (earth, air, fire, and water) and largely fought among themselves for eons.

During the First Age of Creation, the lord of fire, Ragnaros, harbored the goal of slaying one of his counterparts' heirs—Prince Thunderaan, the Prince of Air—and thus further developing his own power and influence. Despite the magnitude of the Firelord's ambitions, Thunderaan remained totally unaware of the threat and was not prepared for the attack.

Ultimately, it proved to be Ragnaros's lieutenants, Geddon and Garr, who betrayed Prince Thunderaan. Before Thunderaan could even react to the situation, Ragnaros himself struck him down with his legendary hammer, Sulfuras. Having triumphed, Ragnaros proceeded to feast upon the fallen lord's very essence, absorbing his power, although he was unable to consume Thunderaan's being entirely. As such, the Firelord stored what remained of the essence within a talisman of elemental binding.

To complete the process, Ragnaros finally shattered this talisman into two separate, flawless pieces, which he assigned to each of his two lieutenants.

Aftermath
Thunderaan's defeat at Ragnaros's hands, though it did not kill him, ensured that he would never appear on Azeroth again for millennia to come. Far in the future, mortal adventurers would eventually reforge the talisman containing the essence of Thunderaan after raiding Ragnaros's Molten Core. These mortals were successful in resummoning Thunderaan and defeat him once more to claim his fabled weapon.

With the advent of the third invasion of the Burning Legion, Prince Thunderaan was finally fully resurrected by members of the Earthen Ring, who enlisted his aid as the restored Windlord in battling the demonic Burning Legion.