The original dragons were fought to release the rain. The hero who fought the dragon was always named "Third" in the local language; he came after King and Prie

The original dragons were fought to release the rain. The hero who fought the dragon was always named "Third" in the local language; he came after King and Priest, who got actual names. In later versions, the dragon had rustled cattle and the hero retrieved them. Those became princesses only very, very recently.