Ải Lậc Cậc is the world-shaping giant of Tai oral tradition in the Northwest, shared between the Black and White Tai. Of colossal size, he is credited with ploughing out the river valleys, heaping up the mountain ranges and opening the first terraced rice fields with his great buffalo, so that peculiar landmarks—solitary hills, bends of the Đà and Nậm Na, immense footprints—are explained as vestiges of his passage. He belongs to the stratum of etiological giant-lore that accounts for the physical setting of the Tai country rather than to the lordly chronicle tradition, and no genealogy links him to the historical ancestor-heroes.