But on Earth, I think my favorite take is the version that says they were a parallel race of hominid sentients that developed along bio-magnetic lines instead of bio-chemical.
Their history started about the same time as humans, but they needed much less in the way of tools, food and shelter. They were also more predatory by nature and hunted by bloodline and territory, so their clans were quicker to build nomad life-style than humans.
They wiped themselves out with in-fighting over which bloodline was the more superior—Atlantis broke up and drowned due to a bloody civil war—and they continued to hunt each other down until the race was no longer viable in the early centuries of A.D.
It is sometimes believed that they were the inspiration for living gods across the globe. It is also speculated that the harsh bias within humans for others of their kind who look or speak differently is due to cross-breeding with this forgotten Atlantean hominid.