Te Mamaku, a chief of Ngāti Hāua-te-rangi, was born probably in the late eighteenth century, at Makakote, near the junction of the Whanganui and Retaruke rivers. His father was Te Ora Kairākau, and his mother was Kahukarewau. Te Mamaku was a grandson of the warrior chief Whakaneke, a descendant of Tamahina. He had connections with Ngāti Maniapoto, Te Āti Awa and Te Āti Haunui-a-Pāpārangi. He was given the name Te Ika-nui-o-roto-o-te-kupenga (the great fish of the net), and was also known as Te Karamū, and Ngātai. Te Mamaku had five wives; they were Tahanga, Te Ngohe, Rea, Anakarangahu, and Hera Matahinewau. Hera was the sister of Te Kere Ngātai-e-rua, a tohunga and leader of Ngāti Tū. Te Mamaku and Hera were married at Pūtiki Wharanui, near the mouth of the Whanganui River, on 24 December 1855. Their son was Wharawhara Te Mamaku.
The pā of Te Mamaku, at Tūhua, on the Ōhura River, north of Taumarunui, commanded a strategic position. Te Mamaku is said to have stated: 'Unuunu te puru o Tūhua māringiringi te wai e puta' (If you withdraw the plug of Tūhua you will be overwhelmed by the flooding hordes of the north).
In the early 1820s Te Mamaku wished his people to join the migration of Te Rauparaha and Ngāti Toa to Kapiti, but was dissuaded by Te Āti Haunui-a-Pāpārangi leader Te Peehi Tūroa. During the siege of Pūtiki by Te Rauparaha in 1829, Te Mamaku fought against Te Rauparaha and his Ngāti Raukawa allies. Te Mamaku and Te Peehi Tūroa were among those who managed to escape death by fleeing upriver.
Te Mamaku was in Wellington in the early 1840s, and by 1846 he had brought his Ngāti Hāua-te-rangi warriors down to join Te Rangihaeata in support of Ngāti Rangatahi in their dispute with the European settlers in the Hutt Valley. On 16 May 1846 Te Mamaku commanded 200 warriors in a dawn attack on troops stationed at Almon Boulcott's farm, near Naenae. The raiders killed six soldiers and wounded four before reinforcements drove them off. The attack succeeded in demoralising the small Pākehā community. Te Mamaku's letters to other Whanganui chiefs requesting that they join him against the Wellington settlers were intercepted. The Whanganui missionary Richard Taylor passed one such letter on to the government, and this information is said to have influenced Governor George Grey's decision to arrest Te Rauparaha.
On his return to the upper Whanganui in late September 1846 Te Mamaku informed the settlers of Whanganui township, who numbered about 200, that he would protect them, but if soldiers were stationed there they would be attacked. Troops were sent to Whanganui in December 1846. After April 1847, when the young Māori from the upper Whanganui who had killed the family of J. A. Gilfillan were executed, there were sporadic raids, burnings and occasional killings on farms on the edge of the small settlement. In May Te Mamaku was one of the leaders of a war party which blockaded the town. Desultory and indecisive fighting culminated in July in an engagement at the foot of St Johns Hill, where two British soldiers were killed and eleven wounded. An equal number of casualties was sustained by the Māori party. Honour was satisfied, and a truce was called. Peace lasted in the district until 1864.
On Christmas Day 1853, at Pūtiki, Te Mamaku was baptised by Richard Taylor. He took the name Hēmi Tōpine (James Stovin). He did not, however, renounce fighting. In the mid 1850s a dispute between Ngāti Hāua-te-rangi and Te Kere Ngātai-e-rua of Ngāti Tū broke out. The dispute may have been caused by an insult, or by argument over a flour mill under construction at Maraekōwhai. There was a battle at the old pā high above Kirikiriroa, on the upper Whanganui, and subsequently a siege of a pā downstream at Puketapu belonging to Ngāti Tū. About eight lives were lost before a truce was called.
In 1857 Te Mamaku was offered the Māori kingship, which he declined, but he joined the King movement in 1858. He did not take part in the battle of Moutoa, on the Whanganui River between Hiruhārama (Jerusalem) and Rānana, in May 1864, when Mātene Te Rangitauira of Taumarunui led Hauhau forces against Māori of the lower Whanganui. However, he supported Te Peehi Pākoro Tūroa (Te Peehi Tūroa's son) and Hauhau forces in the battle at Ōhoutahi, below Pipiriki, in February 1865.
In 1873 the upper Whanganui resident magistrate, Richard Woon, described Te Mamaku as 'our old friend' and 'all in favour of peace'. He was widely respected for his intelligence and mana. Woon confided to Donald McLean, the native minister, that 'I much prefer such men as Mamaku…as they have a nice sense of humour about them that you fail to perceive in younger chiefs.' Te Mamaku joined Tōpia Tūroa in opposition to Te Kooti, but did not encourage European settlement above the King Country boundary line. In late 1878 Te Mamaku and Te Kere warned the land-grabbing millwright and powder-maker William Moffatt that he was not to return to the King Country. Moffatt's failure to heed the advice led to his execution in 1880. That year Te Mamaku joined Te Keepa Te Rangihiwinui in a trust, which aimed to protect from sale two million acres of Māori land to the east of the central Whanganui River.
In the last years of his life Te Mamaku embraced the changes which were being thrust on the Whanganui King Country region. He urged that a steamboat be placed on the river, and that a school be started in Taumarunui. He was said to be almost 100 years of age when he died in late June 1887 at Tāwhata, below Taumarunui. He is buried at Makakote.