Tumu-nui is the name of several figures in Tahitan mythology.

This is the name is a major god in the creation myth. There, he and his wife Paparaharaha were responsible for creating the pillars that hold up the sky (Rumia).

This is also the name of the uncle of the hero Rata

Rata (Tahitian mythology)

Rata, in Tahitian mythology, is said to have become king of Tahiti when his uncle, king Tumu-nui, and his father Vahieroa are swallowed by a great clam while they are on their way to Pitcairn. When he reaches adulthood, Rata plans to avenge his father. As in the Tuamotuan version, Rata...

. He was king of Tahiti. When he was lost at sea, his nephew Rata became king.