The story of the Eternal Wanderer is primary explained in the book of flood and in the Sermon of Vatras the water mage.
Chosen one
Barely over a thousand years ago the Eternal Wanderer lead a tribe of nomads when Innos spoke to him and made him his servant. Innos gave him a scepter instead of his staff and offered him parts of his divine power, the magic of fire. Equipped with this power Innos ordered him to fight the doings and the chosen one of Beliar.
Settling down
The Wanderer and his followers became the people of Varant and built big cities and five large temples in honor of Innos. But Beliar screamed in rage when the people started to erect a portal for Innos, so the could rule the world forever. He spoke to another being and wanted to choose another sevant for himself.
The flood
But Adanos saw the balance in danger and sent the great flood and washed this being away from the face of the earth. But the flood also destroyed animals and plants and the people of Varant.
This is when Adanos in his grief banished his brothers from his realm.
End of the fight
The Wanderer and the chosen one of Beliars survived the flood and fought until the human slew the beast and banished it ... for a time. Adanos bade his brother Innos to leave some of his divine power behind, so another chosen one could fight the beast if it returns. And Innos did so.
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