In Chrétien de Troyes’ Erec et Enide, Lac is King of Outer-Wales, a realm which contains the cities of Roadan and Montreval. According to the Vulgate Merlin, King Lac rules over Orcanie the Great. Lac’s kingdom is unnamed in the Post-Vulgate Arthurian Cycle.
According to Erec et Enide, King Lac dies of old age and his son Erec is made ruler of Lac’s kingdom by King Arthur.
According to the Post-Vulgate Cycle and Guiron the Courteous, King Lac, even while a king, is a prominent Knight of the Round Table. The Post-Vulgate Quest of the Holy Grail relates that Lac was slain by the unnamed sons of his brother King Dirac who then take over the rule of Lac’s kingdom. Erec is slain by Gawain before he can even attempt to regain his father’s kingdom