Niumataiwalu was the founder of the Vuanirewa dynasty, a noble clan of the Lau Islands (in Fiji) from which the Tui Nayau is chosen. Niumataiwalu was the son of Delainavugalei, a high-ranking noble of the island of Nayau and Lakeba.
Qoma was the elder brother of Delaivugalei; the latter the father of Niumataiwalu. Both were sons of Kalouyalewa, who was the brother of Buivaroro (the second Tui Nayau), and they had one sister, Adi Keletu that was married to Noco in Rewa. Kalouyalewa's father was Tuivanuakula 2 and otherwise known as Tuinaosara. Niumataiwalu killed his uncle Qoma and his sons, in retribution for the murder of his own parents and sibling. This series of events eventually paved the way for his descendants overlordship of both these islands and the rest of Lau. In establishing his dynasty he is often recognised as the first Vuanirewa high chief or Roko Sau of the Lau Islands.
Traditional legend has it that Niumataiwalu was renowned not only for his valour in battle but also for his beauty. This latter attribute would eventually attract the attention of one of the noble ladies of Bau, causing an illicit affair and leading to his eventual demise, for the lady was the Radini Levuka, wife of the Vunivalu or Paramount Chief of the Kubuna Confederacy. The adulterous affair did not come to light until the Radini Levuka realized she was pregnant, and though she and her child, Banuve Baleivavalagi, were not harmed, the Vunivalu bided his time and planned revenge for this offence upon himself and his noble household. He tendered the support of two Ono-i-Lau chiefs, Saunikalou and Radua who were visiting Bau at the time and were subjects of Niumataiwalu, by presenting them with a tabua made of black stone and requesting for the murder of their overlord.
In time Niumataiwalu visited Matokano Village in Ono-i-Lau and a welcoming feast was accordingly prepared for him. This was also an occasion the two conspiring chiefs saw as an opportunity to exact the earlier instructions of the Vunivalu. As all weapons were forbidden in the area where the kava ceremony was to take place, Saunikalou hid a war club in a hollowed out banana stem and instructed his young son to play with it as a toy where the ceremony occurred. When the first appropriations of kava drink was being given to Niumataiwalu, unsuspecting he lowered his head, at which the same time Saunikalou grabbed the hidden weapon and struck him. The first blow did not kill Niumataiwalu, and he fled towards the beach in the hope of gaining aid from some of his men. He was however overpowered by Saunikalou and his men, and was clubbed to death.