Shukfir
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The Slavs and Greeks had different gods; as far as I know, the Mongols didn't.
Well, maybe. But at least Heaven and Earth are the oldest gods of many peoples.
In Greek mythology, Uranus and Gaia gave birth to all the other gods.
Or, for example, the New Zealand tribe, the Maori, believes that the gods were born from the union of Rangi (Sky Father) and Papa-tū-ā-nuku (Earth Mother).