A heathen king who led raids into King Mark’s England in the Icelandic Saga af Tristram ok Ísodd.
Tristan met him in combat, but with a small force. Near defeat, Tristan swore before God to end his affair with Isolde if he should prevail. Fúlcus was soon dead, and Tristan left England for good to assume the throne of Spain.
Source
Saga af Tristram ok Isodd | 14th century