The King of Erminia and Tristan’s father in the Middle-English Sir Tristrem, analogous to Rivalin in the romance of Gottfried von Strassburg.
After fathering Tristan on Blancheflor, the sister of King Mark, Rouland was slain in a war against Duke Morgan. His steward, Rohand, raised Tristan, and the latter avenged his death.
His counterpart in the Prose Tristan is Meliadus.
Source
Sir Tristrem | c. 1300