Elemental Sundering

The Elemental Sundering was a 5000 years long battle, fought between elementals at the core of Azeroth.

At some point during the war, Ragnaros defeated Thunderaan and bound his essence into a talisman, which he divided between his lieutenants.

Description
The Lieutenants of Ragnaros, Geddon and Garr, perpetrated the betrayal against Thunderaan, who was caught unaware. The Firelord's advances were wholly unknown to Thunderaan, and before he could react, Sulfuras, legendary hammer of Ragnaros, struck an unmerciful blow, and Thunderaan fell, utterly defeated.

The Firelord feasted upon the essence of Thunderaan, but was unable to consume him entirely. He stored what little remained of Thunderaan's essence within a talisman of elemental binding. Ragnaros then shattered the talisman in two flawless pieces, and assigned them to his Lieutenants.