The Elemental Kings were powers summoned by some humans ages ago, in order to fight against the "tiranny" of the Ancient Spirits.
These powerful spirits of the land got the help of the Forgotten Gods in order to gain the strenght to beat the Ancient Spirits.
It said that one of the Forgotten God sacrificed his essence in order to give strenght to this demigods.
The Elemental Kings reincarnate continously in mortal bodies (usually the ones of jinns).
They are currently seen as the supreme authority of the various elemental Kingdoms. They have a spiritual role as well. The expect some worship from their followers and in exchange they help their people with advice and guidance on how to run they societies successfully.
PYROS: King of Fire
GEA: Queen of Earth
SEVIRON: God of wind and travel, storms, Navigation (previously mainly air)
HYDROS: King of Water (killed by Dragonsoul wizards during the wars against the Kings)