What is "turgesius"

Turgesius (died 845) (also called Turgeis, Tuirgeis, Turges, and Thorgest) was a Viking chief active in Ireland during the 9th-century. Turgesius Island, the principal island on Lough Lene, is named after him. It is not at all clear whether the names in the Irish annals represent the Old Norse Thurgestr or Old Danish Thorgísl. John O'Donovan and Charles Haliday independently identified him with Ragnar Loðbrók, but the identification is not generally accepted.