Iwikau, the second surviving son of Herea, the first Te Heuheu Tūkino, and the child of Rangiaho, of Ngāti Maniapoto, was born late in the eighteenth century. Like his older brother, Mananui, he became a great warrior, known for drawing first blood in battle.
In January 1840, accompanied by Te Korohiko, he travelled to the Bay of Islands with CMS missionary Henry Williams to take part in the deliberations about the Treaty of Waitangi. Impressed by Williams's explanation of the treaty, he and Te Korohiko signed, although they did not have the authority to commit the tribe. When, several months later, a copy of the treaty was discussed at Rotorua, Mananui repudiated Iwikau's action, but the Ngāti Tūwharetoa signatures remained on the treaty nevertheless.
After he returned from the north, Iwikau built an ornamented house, close to the waterfall at Waihī, at the southern end of Lake Taupō; it was painted red with clay from the hot springs near Te Rapa. He had been so impressed with the hospitality he had received in the north that he named this house Tāpeka, after the place where his hosts lived at Kororāreka (Russell).
After his brother's death in 1846 Iwikau was chosen to succeed him; Mananui's son, Horonuku (also called Patatai), was considered too inexperienced. Iwikau went to live at Pūkawa, in the territory of Ngāti Manunui, the hapū of his senior wife, Ruingārangi (or Mōrunga); Pūkawa became his principal pā. For a time there was conflict between Iwikau and Te Herekiekie of Tokaanu over the issue of leadership, but they were reconciled by the missionary Thomas Grace. Iwikau had long requested a missionary and Grace selected a site for a mission at Taupō in the early 1850s. In April 1855 he settled with his family at Pūkawa, under the protection of Iwikau. According to the geologist Ferdinand von Hochstetter, who visited Iwikau a few years later, the Ngāti Tūwharetoa leader was 'not averse to Christianity' but feared that baptism would bring about a loss of influence and authority. He would also be obliged to give up several of his wives before baptism. Although he never became a Christian, Iwikau attended church services regularly and Grace respected him as 'friend and protector'.
When he visited Auckland in the late 1840s, Iwikau became acquainted with Governor George Grey. In 1850 Grey visited Pūkawa, and, in recognition of Iwikau's loyalty to the Queen, presented him with a flag similar in design to that given to the northern tribes by William IV in 1834. Grey admired his richly carved food storehouse and remarked that all chiefs should have such storehouses as a sign of their standing and generosity. When later this storehouse was destroyed by fire, Iwikau, remembering Grey's words, set out to build another, larger and more elaborately ornamented. After four years of building, it was completed in 1855, and named Hīnana. To demonstrate his mana, which was being challenged by some of Ngāti Te Aho, Iwikau invited people from all the major tribes to its opening in November 1856. After his death it was re-erected at Waihī. It is now in the Canterbury Museum, while at Waihī village the dining house is called Hīnana.
During the 1850s Iwikau sought both to restrain Māori protest and to support the growing grievances over the loss of land. Late in 1856 he convened at Pūkawa a meeting opposed to further land sales; an ardent proponent of Māori nationalism, he also encouraged the movement to set up a Māori king. He did not seek the position for himself and supported the installation of Pōtatau Te Wherowhero at Ngāruawāhia in 1858. However, when the Taranaki war broke out in 1860, he tried to prevent Ngāti Tūwharetoa from joining, fearing that the tribe's lands would be threatened.
Iwikau, towards the end of his life, was described by Hochstetter as 'of middle size, delicately rather than robustly built, wearing his black hair in long locks.' He had a 'beardless face,…imperfectly tattooed upon the right cheek, with…small sparkling eyes'. He died in October 1862, and is buried close to the meeting house, Tāpeka, at Waihī. He was survived by Ruingārangi, with whom he had had a daughter, Whenerata, and a son, Iwikau. He is remembered for his laments, especially the one that some say he composed on the death of his brother, Mananui, in a landslide.