Ancients

A generation filled with different unique creatures that contained untold amounts of power oftentimes rivaling or surpassing the gods. Creatures like this include the Collosi Ancients, the tarrasque, the Kraken of the Deep, or the High Dragons from the Ageroth Mountains.
Ancients are oftentimes revered as gods and may even hold their own domain, but unlike the gods none of their power ever comes from worship or being known. The Ancients are completely biological and real, and thus this makes them dangerous to the gods who are oftentimes bound by religious rules and bounds. They were also a threat to the impending civilized races as they began their stretch of dominance across The Continent. 
Throughout the rise of the Common Races   the Ancients began to be hunted down by armies and legendary parties to secure regions and gain the magical elements these creatures were made of. This caused an uptick in the use of magic from the Ancients who typically never had a need for it. Scholars say the Ancients that were unable to hide in Tomeria anymore sought out magic to carve out their own pocket dimensions to await the collapse of gods and civilized folk.
In the Exploration Era and beyond there is no known sightings of Ancients. While there are several recorded killings of the weaker Ancients, scholars doubt that most are dead or gone and are simply in deep slumber or hiding as they wait for the civilized races to crumble so they can more easily reassert their domain back to how it was before the gods and civilized folk.