Gwallauc Marchauc Trin, King of Elmet
(Born c.AD 510)
(Welsh: Gwallog; Latin: Wallocus; English: Waltock)

There are two surviving poems in praise of King Lleinauc of Elmet's son, Gwallauc the Battle Horseman, and it is one of these that identifies the kingdom which was ruled by his line. In En env Gvledic nef gorchordyon, he is called "a judge over Elmet".

Gwallauc's reign was at its height in the late 6th century, when he allied himself to his cousin, Urien Rheged, and his confederation of British kings that included Kings Riderch Hael of Strathclyde and probably Morcant Bulc of Bryneich. Together, they caused much discomfort to King Hussa of Bernicia and his Anglo-Saxon armies. Gwallauc was present at the Siege of Ynys Metcaut, against him, in 590. It is thought he may have contributed a sea-faring contingent to the coalition. The alliance fell apart soon afterwards but Gwallauc seems to have still managed to keep the Anglo-Saxons away from his kingdom. He was succeeded in Elmet by his son, Ceretic.