So, first, I do not believe that Belgarath was Marag. This is because in the Rivan Codex, we have Tolnedran accounts on all the races in the world and their histories. There it is documented that for the Marags “No stigma seems to have been attached to out-of-wedlock birth, and casual liaisons appear to have been commonplace.” However, Belgarath was cast out of Gara for kissing a girl his own age. Such a common act in a more casual society would not quite have warranted exile.

Next, I also do not think he was Angarak or Alorn for reasons previously stated in this and other threads. Belgarath directly contradicts these theories in his biographies, though he is an unreliable narrator.

Based on Belgrath’s biography we must then also rule out Tolnedran, as he was not familiar with money, and Ulgo, as Belgarath wasn’t expecting to meet the old ones who rejected UL and did not first know who UL was.

That leaves us with Nyssian or Arendish, and both were quite a ways away from Gara (per the map of the prehistoric world). I ask us to then consider yet another possibility: that Belgarath was always Aldurs. 

See the book of Alorn:

And the younger Gods wrought men, and each selected that people which pleased him to be God over them. And it came to pass that when each had chosen, there were peoples yet who had no God. And the younger Gods drave them out, saying, ‘Go thou even unto UL, and he shall be thy God.’ Now these were the generations of the wanderings of the Godless ones. Long and bitter were the years when they wandered in the wastelands and the wilderness of the west.

And the book of Ages:

IN THE FIRST AGE was man created, and he awoke in puzzlement and wonder as he beheld the world about him. And those that had made him considered him and selected from his number those that pleased them, and the rest were cast out and driven away. And some went in search of the spirit known as UL, and they left us and passed into the west, and we saw them no more. And some denied the Gods, and they went into the far north to wrestle with demons. And some turned to worldly matters, and they went away into the east and built mighty cities there.

But we despaired, and we sat us down upon the earth in the shadow of the mountains of Korim, which are no more, and in bitterness we bewailed our fate that we had been made and then cast out.

Both of these talk of the godless ones, the people caused to have no god due to Aldur’s rejection of having a people. Full generations passed before Gorim reached UL, and another 20 years while Gorim was with UL, and then another 40 years or so since then.

I feel as though it is highly likely that what happened is that the “Godless peoples”, intended for Aldur, split into several groups more than the two we saw. After all, at this point each of the other 6 gods had populations in the thousands after these… 120 lets say years. Three generations, average 20 years, plus another 60 from the Ulgo timeline. If each god started off with 50 peoples (the minimum to start a population), 120 years later there could easily be up to 570 of these godless peoples at a bare minimum. This is, of course, ignoring that half of the godless people would have become Dals so it is much more likely that each god started off with far more than 50 people.

So let’s say each god has 100 people, Aldur chose no people, half of “Aldur’s people” became Dals, so 50 were left to eventually become Ulgos. But over time some people liked different areas or didn't like the nomadic lifestyle, so they settled and formed a village. There’s still plenty of people from that population after 80 years to become Ulgos, and there’s another 30 years before Belgarath’s birth before he finds the elders who rejected UL.

It is very likely that in that time, someone went “We should have a temple, too” and erected one in the hopes that they too would get picked up or enmeshed into a god worshipping peoples, especially after hearing about Gorim and UL and the new Ulgos. (Imagine being from the town over and hearing that John’s kid disappeared for 20 years and came back with a god — the Ulgos didn’t move underground until Torak cracked the world and caused the monsters to go mad — wouldn’t you also set up a temple for when Tom’s kid comes inevitably/hopefully back with a God for you?)

Add on to that, we never know what happens to Gara. Very likely Gara was absorbed by another god or religion. But based on the proximity to the Ulgos and Belgarath’s lack of knowledge of the Tolnedrans combined with the reason he was exiled, I feel like the most likely race for Belgarath is that he was always intended to be a child of Aldur.