The D&D 5e Monster Manual says this in the aboleth section:
ABOLETH: Before the coming of the gods, aboleths lurked in primordial oceans and underground lakes. They reached out with their minds and seized control of the burgeoning life-forms of the mortal realm, making those creatures their slaves. Their dominance made them like gods. Then the true gods appeared, smashing the aboleths' empire and freeing their slaves. Aboleths have never forgotten.
This seems to state that besides the aboleths, other mortal beings existed before the gods.
Which races were these?
I'm specifically looking for answers from the Forgotten Realms setting.