King Hiss and Serpos in Iranian mythology:
https://en.wikipedia.org/wiki/Zahhak"Aži Dahāka is the most significant and long-lasting of the ažis of the Avesta, the earliest religious texts of Zoroastrianism. He is described as a monster with three mouths, six eyes, and three heads, cunning, strong, and demonic.
Feyredon is said to have been endowed with the divine radiance of kings (Khvarenah, New Persian farr) for life, and was able to defeat Dahāg, striking him with a mace. However, when he did so, vermin (snakes, insects and the like) emerged from the wounds, and the god Ormazd told him not to kill Dahāg, lest the world become infested with these creatures. Instead, Frēdōn chained Dahāg up and imprisoned him on the mythical Mt. Damāvand."
In the epic Shahnameh, Shah Zahhak has a human head and limbs but also two snakes growing from his shoulders.
"a blacksmith named Kāva (Kaveh) speaks out in anger for his children having been murdered to feed Zahhāk's snakes, and for his final remaining son being sentenced to the same fate. ... Fereydun strikes Zahhāk down with his ox-headed mace, but does not kill him; on the advice of an angel, he binds Zahhāk and imprisons him in a cave underneath Mount Damāvand."
