Marnbil is the founding ancestral lawgiver of the Lardil people of Mornington Island. In the cycle recorded by Goobalathaldin (Dick Roughsey) and analysed by David McKnight, Marnbil is the young warrior-leader of the first ancestors who came from the west to settle the Wellesley Islands; with his wife Gin-Gin and her uncle Dewallewal he created and named the animals, built the first rock-walled fish traps, dug the freshwater wells, and laid down the law and country of the Lardil, including the foundational obligation to share food. On the last day of their journey he returned to find Dewallewal with Gin-Gin and speared him; Dewallewal's death-throes raised the first Bora ground and brought mortality upon the people. The mineralised remains of the three ancestors are identified with a reef of sharp rocks off the Mornington Island coast.