Who is native to Alidor?
The races of Alidor are a mixed bunch. Races from the Core Rules books are most common; found almost everywhere. Races from the Expanded Psionics Handbook and the Planar Handbook tend to live in isolated communities or are just passing through on one of their jaunts through the planes. The Mul are unique to Alidor, some say the magics required to create Mul came from another world most likely Athas a dusty waste known best for its cruel sorcerer king rulers.
How did the races arrive?
There are no known native races to Alidor. It is clear to any traveler that the ruins found along trade routes where the work of some ancient advanced people. None of these people are known to exist today. Though if you question an orc prior to putting it out of it's misery, It would have something more to say on the origins of the ruins. Orcs claim to be ancestors of the people that once ruled Alidor. Most known sites of the ancients have been luted to the point that no discernible evidence remains to support the orcs claims. Even the oldest sentient beings known to exist and maintain cultural histories, dragons, elan and elves do not know or remember or wish to discuss the ancient history of the world.
Most civil beings arrived via planar travel as groups of colonists. Dragons claim to have been lead here by Surma. They say when they arrived they found great cities void of all their inhabitants but still full of all the worldly goods dragons enjoy most just laying there for the taking. To the dragons Alidor was utopia all the gold and treasures they could ever imagine and no one to hassle them about it. Until of corse the pickings became slim. War among the dragons destroyed the permanent settlements of the ancients save one... the city that today is called Alidor.
Dwarves, elves, humans and orcs where brought here as slaves for the dragons. Bariaur came here to fight evil. Buomman found tranquillity in the mountains near the Vale of Ingersol. The dromites found comfort among the wandering turtle cities of Alidor, they spend their days grooming the tortoises and assisting with general maintenance. Many elan where willed into existence by the tortoises. Other elan where created though ritual on some other world and then traveled here.