Nanion is the leader of the people of D'Or, a city that was founded by foreigners to Deltora. It was named after Nanion's family name. He is a descendant of the people of Fleet, a town on the island of Dorne, who fled their island a thousand years ago and settled in Deltora during the reign of Queen Adina.
Nanion was cursed by Thaegan and turned into the sea monster Soldeen to guard the ruby. His wife was turned to stone and his people were transformed into various creatures residing in the Lake of Tears created by Thaegan. A hundred years would pass before Lief, Barda and Jasmine would lift Nanion's curse. Though he battles Lief, Soldeen regains his memories as Nanion and helps in getting the Ruby before Thaegan arrives. Upon Thaegan's death, the Lake dries up and both Nanion and D'Or are restored to their original forms.