Before the Great Old Ones interfered there were three sentient species on FirstWorld. The oldest was a race of sentient trees of which the One Tree and the Forbidden Forest at Elvenhome are the main remaining examples.
There were two distinct races of people and the Ancient Ones are the non-humans. When the Great Old Ones genetically enhanced humankind, they became more aggressive and they almost extinguished the Ancient Ones.
They were a gentle people. Their distinguishing features include only three digits and different coloured eyes – grey & green. There was some interbreeding with humans and so some of their genes remain in the human genome. Julie carries these genes.
There are at least two remaining Ancient Ones who have survived. It is not known whether they are immortals, rather it is thought they exist outside of normal time and space. Marduk, the Gardener of Eden, only appears infrequently in Elvenhome. The Captain of the Ship of Souls exists in Limbo. Neither of them was aware of the other’s existence until Simon informed them.