Old Ones

The Old Ones were an impossibly ancient race of alien beings that arrived in Plethira around 400,000 years ago. Their appearance is unknown, but their cities were said to be magnificent and gigantic beyond imagination. They wiped out countless species as they fed their populations, and from this resulted some kind of cataclysm that wiped all of them from the face of the earth within the space of one hundred years. This provoked them to create the race known as the Eldar.