In my Masks of the Imperium campaign, the planet was the body of a murdered goddess, with the moon as her decapitated head. There was no progenitor "race" per se, but the first inhabitants were a large number of offshoots from her - not children exactly which would imply godhood, something less. These lived a long time and had a lot of influence, and eventually all died out. There is one still around as a ridiculously old vampire that leads an Aztec/Mayan inspired gnome wereleopard empire that lawful and humane - and the penalty for any infraction is an amount of blood. The others are gone, but fossilized echoes of their ghosts were shaped into the titular Masks of the Imperium.
(But mind you, the goddess was brought to a limbo plane with nothing in it to murder -- there are other civilizations and races elsewhere. The Feywild played a big part, and an elder brain and illithid colony from a crashed nautiloid that was attempting to eat the petrified brain of the goddess deep inside the moon attempting apotheosis. So even that precursor "race" was just for this plane.)
In my Errantas campaigns I have a unique cosmology where all of the material planes bobbed independently in the four elemental planes, and the prime material the campaigns started on had a "thin shell" making it easier to get to when the bubbles pressed against each other, so the majority of races were fleeing genocide or the like from their own worlds and were brought here by their gods. Which made things interesting, such as two orcs civilizations that came from completely different planes, and elves went around in demi-planes called Courts that they could control in the elemental planes. (This started with 3ed, before the Feywild was codified.) The original race living on this world was an underdark variant of the halfling, and all of the surface halflings were unknowingly decended from them.