Seven Kingdoms: Seowyn's Crossing
Early in the first years of the Dawn War, the Primordials realized that they were at a disadvantage in fighting the Gods. The Primordials were not very imaginative in their creation of races, so they were aided primarily by the giants, while the Gods had the various mortal races of Tol to help them fight.
Recognizing their need for armies to fight the armies of the Gods, the Primordials gathered Elemental spirits that were already manifest in the realm of the Elemental Chaos. They persuaded the spirits to fight, encased in armor and wielding weapons that let them more effectively affect the people of Tol. Tempted by dreams of conquest and wanting to punish the Gods for their arrogance, the elementals agreed, becoming armies of Myrmidons.
The armies of the Primordials wreaked havoc among the mortals of Tol until the Gods intervened by creating their own elite armies in the forms of the angelic host. After the war was over, the myrmidons continued to exist, bound by the pacts they’d made. Occasionally, a mortal or immortal entity enlists their aid in some cause or another.