Primordial

The Primordials, also known as elemental titans, primordial titans, or simply the titans, were a race of great, ancient elementals that once inhabited the Material Plane.

The Founding
Prior to the arrival of the gods into Exandria, the Primordials claimed the world as their own and dwelt deep beneath its surface. During the Founding, the gods created the first mortals, including the first humanoids and dragons. After this, the Primordials rose from the earth to attack them. During the ensuing struggle, the gods split into the Prime Deities, who wanted to fight the Primordials and protect their creations, and the Betrayer Gods, who wished to join the Primordials and give the world back over to the chaos. In the end, the Prime Deities were victorious, and the Betrayer Gods were individually imprisoned or banished while the Primordials were destroyed and scattered to their own planes. One such titan, the Molten Titan, was felled by elves at the end of the Founding and was subsequently sealed within and consumed by the earth, forming the Daggerbay Mountains of Tal'Dorei. Two others, Emperor Rau'shan and Empress Ka'Mort, were sealed beneath Toramunda by Pelor and Melora during the Schism.

The Calamity
Asmodeus's plan for the Calamity was to use the act of the Replenishment to release Rau'shan and Ka'Mort from beneath Mount Ygora and fight the mortals of Exandria alongside them. This would have destroyed Exandria. The Ring of Brass, upon learning of this prophecy, aided Laerryn Coramar-Seelie in modifying her Astral Leywright to banish Rau'shan and Ka'Mort across the planes.

The Titanstone Knuckles, one of the Vestiges of Divergence, was forged from the heartstone of an earth titan.

Post-Divergence
During the Icelost Years, Errevon the Rimelord, an ice titan, lead an invasion of Tal'Dorei before being resealed in the Frostfell. It is not confirmed that Errevon was a primordial, but he is speculated by Exandrian scholars to have been one who escaped the war during the Founding.

Roughly 15 years prior to the events of the Chroma Conclave, the heartstone of a fire titan, called a soul anchor, was attached to Thordak to seal him in the Elemental Plane of Fire.

After his ascent to godhood, Vecna raised an Earth Titan, atop the shoulders of which rested the city of Thar Amphala. Vox Machina traveled through this titan so that they could fight Vecna.