Sichelin
King of Norway and grandfather of Lot in Geoffrey’s Historia.
When he died, he left his kingdom to his grandson, but a lord named Riculf seized it, prompting Arthur to conquer Norway and restore it to Lot.
In De Ortu Waluuanii, Sichelm is Lot’s uncle rather than his grandfather. Having been conquered by Uther Pendragon, Sichelm was forced to send Lot to Uther’s court for rearing.
Sources
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
De Ortu Waluuanii Nepotis Arturi | Late 13th century