During the Christianization of the Slavs many of their myths became rebranded with Christian imagery. Perun was syncretized into God and Veles into Satan for this myth.
But, Veles was not always evil, he was also syncretized into St. Nicholaus who in the myths protected the poor farmers and animals from St. Elias the Thunderer (a syncretized version of Perun).
The battle between Perun and Veles is not good verses evil, but merely the oppositional forces of Order (Perun) and Chaos (Veles).
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