Gurmun the Gay
As a bitter enemy of King Mark of Cornwall, he sent his best knight, Morholt, to menace Cornwall and collect a tribute. Tristan traveled to Ireland under the name 'Tantris' and killed a dragon. When Gurmun learned of this noble deed - and then of Tristanís true identity - he agreed to peace between Ireland and Cornwall and he gave his daughter to Mark.
His character in other romances is called Anguish.
Gormund | The Legend of King Arthur