Te Whatanui, sometimes known as Te Whata, Tohe-a-Pare, or Tohe-ata, was the son of Tihao of Ngati Huia and Ngati Parewahawaha, two hapu of Ngati Raukawa. His mother was Pareraukawa, elder sister of Hape or Hape-ki-tu-a-rangi of Ngati Raukawa and Ngati Huia. Hape died at Maungatautari, the heartland of Ngati Raukawa ancestral territory, which stretched eastwards from Maungatautari towards the Patetere plateau, about the turn of the nineteenth century, when Te Whatanui was still young. Hape's own sons were also young, and Te Whatanui and the other hereditary chiefs of Ngati Raukawa made no protest when Te Rauparaha, a contemporary of Te Whatanui and belonging to Ngati Huia through his mother, claimed the succession to Hape's mana, and later married his widow. Effective leadership devolved on Te Whatanui and other chiefs; Te Whatanui was to be regarded as the leading chief of Ngati Raukawa.
Ngati Raukawa were increasingly threatened as the wars between Waikato and the Kawhia tribes continued in the early nineteenth century. After Te Rauparaha had led the first migration of his people to Taranaki about 1821, he returned to attempt to recruit allies to join him in the resettlement of his people on the Kapiti coast. He turned to Ngati Raukawa first, but Te Whatanui and other chiefs refused his invitation. However, when Te Rauparaha carried the same invitation to Te Waru of Ngai Te Rangi, at Tauranga, to other chiefs, and finally to Ngati Whakaue, at Rotorua, Te Whatanui went with him. There, perhaps late in 1821, Te Whatanui urged Ngati Whakaue and Tuhourangi to kill any Nga Puhi they might meet, because Wheturoa, his nephew, had been killed that year by Nga Puhi, at Te Totara, in the Thames district. His wishes were heeded, and the killing of many Nga Puhi by Ngati Whakaue and Tuhourangi led to the mass Nga Puhi attack on Mokoia in 1823.
Although he did not accept Te Rauparaha's invitation to resettle in the Cook Strait region, Te Whatanui was determined to establish a new home for his people. His preference was for Heretaunga (Hawke's Bay). On the way there he took a large party including women and children to Taupo. Almost at once his fighting force joined that of Mananui Te Heuheu Tukino II in taking the pa Te Roto-a-Tara, near present day Te Aute College. While Ngati Raukawa were settled at Taupo, the chief Te Wharerangi was killed in the Rotoaira district by Te Ati Haunui-a-Paparangi of upper Wanganui. Te Whatanui then invaded Wanganui, killing Hekawai. Te Ati Haunui-a-Paparangi retaliated, inflicting a heavy defeat on Ngati Raukawa, and killing Te Rua-maioro. To avenge this death Te Whatanui campaigned against Ngati Te Upokoiri and Ngati Hinemanu in the upper Rangitikei district, defeating them at Te Otaparoto.
After the victory at Te Roto-a-Tara, Ngati Te Whatu-i-apiti had retreated with Nga Puhi to Nukutaurua on the Mahia peninsula and much of Heretaunga was deserted. Te Whatanui made his first serious attempt to establish a new home there for his people. He had been invited to come by Te Kaihou, the sister of Te Ringanohu of Ngati Te Kikiri, a hapu of Ngati Te Whatu-i-apiti, to assist her people against Ngati Te Upokoiri. Te Whatanui brought a party of 150 to 200 fighting men. Those chiefs of Heretaunga, mostly Ngati Kahungunu, who had not retreated to Nukutaurua, fortified themselves at the Ahuriri pa, Te Pakake. They were prepared to tolerate Te Whatanui if he would help to defend Te Pakake. But Te Whatanui preferred to establish his own pa at Puketapu, on the Tutaekuri River. At first Ngati Raukawa lived in peace with the local people. But tensions developed, especially over resources. Te Whatanui was overheard planning to bring the rest of his people from Taupo.
The chiefs of Heretaunga began to assemble their forces at Te Pakake, sending out messages to all who still lived nearby. Puketapu was attacked from two directions; some of its defenders tried to escape by leaping down a cliff into the river. Te Whatanui was chased by Te Paratene Tipitaha, a younger brother of Tuaha of Waimarama. He caught hold of Te Whatanui's garments; Te Whatanui tore them off and escaped naked, hiding in the water until dark. Some of the leading women of Ngati Raukawa, including one of Te Whatanui's wives and at least one son, were captured; some later escaped.
In revenge for his defeat at Puketapu, Te Whatanui and his war party joined Mananui Te Heuheu and other chiefs in their attack on Te Wera Hauraki, Te Pareihe, and their people in the pa later known as Kai-uku in the Mahia district. Te Whatanui's ally, Te Momo-a-Irawaru of Ngati Te Kohera and Ngati Raukawa, was killed at Kahotea pa near Te Roto-a-Tara.
After his defeats in Hawke's Bay Te Whatanui turned his attention to the Kapiti Coast. In the later 1820s he brought a large body of Ngati Raukawa to the Manawatu coast by way of Rangipo, Turakina and Rangitikei. On their way Ngati Raukawa surprised and killed small parties of local people, including Te Whareki of Ngati Apa.
Te Whatanui and his party were welcomed by Te Rauparaha, and may have lived on Kapiti Island for some years. Later Te Rauparaha, because of his relationship to Te Whatanui, made him a gift of Manawatu, the Horowhenua district and Otaki. He is said to have remarked: 'Live at Otaki, but be careful of Muaupoko'. (Muaupoko were one of the peoples already living in that district.) Te Whatanui is said to have replied: 'You meddled with them; I shall not…I shall live in peace.' However, Ngati Apa were planning to attack Ngati Raukawa because of the deaths they had caused on their migration. While Te Whatanui's party advanced along the beach to Ohau, Ngati Apa were trailing them inland. They had left their women and children at the Horowhenua pa, Hotuiti; Te Whatanui got there first, and captured at least twelve Ngati Apa women. He set one free to bear a message of peace to her chiefs. Ngati Apa remained suspicious; they attempted to capture a nephew of Te Whatanui; this incident put Ngati Raukawa on their guard. Te Whatanui brought his force downriver by canoe, his people firing their weapons at both sides of the river. Te Whatanui called out to Ngati Apa that he wanted to make peace; he assured them that there would be no treachery: 'There will be no evil done, Ngati Apa'. More captives were released as a sign of good faith.
Te Whatanui succeeded in making peace with Rangitane, Ngati Apa and Muaupoko. He made a famous speech to the 100 or so Muaupoko still living at Horowhenua, survivors of clashes with Ngati Toa, offering to be the rata tree that sheltered them. He allowed Ngati Apa to share Ngati Raukawa's territory with no loss of mana; later his generosity was to cost Ngati Raukawa dearly when claims came before the Native Land Court. He settled at the pa Rau-matangi at Horowhenua. After his people were established, Te Whatanui led a war party through the Manawatu Gorge to avenge his defeats in Hawke's Bay. Aided by Ngati Pakapaka and Ngati Mutuahi, two hapu of Rangitane, he raided as far north as Tangoio. Two high-ranked women, Paeroa and Kutia of Heretaunga, were killed by this war party. In response, a combined Hawke's Bay, Wairarapa and Nga Puhi force attacked Rangitane living in and near the Manawatu Gorge. About 1829 Rangitane, Muaupoko, Ngati Apa and Ngati Te Upokoiri were invited to a feast by Te Puoho-o-te-rangi of Ngati Tama. Te Whatanui was true to his word and warned them not to go. They ignored his advice, and were massacred by Te Ati Awa.
After the arrival of Ngati Raukawa tensions developed between the migrant tribes themselves. A fatal argument over potatoes stolen at Waitohu by Te Ati Awa triggered the important battle between them and Ngati Raukawa known as Haowhenua, about 1834. Mananui Te Heuheu of Taupo and other northern chiefs came to the aid of Te Whatanui. His kindness to the local people brought its reward; Ngati Raukawa were assisted by Rangitane, Muaupoko and Ngati Apa. Nevertheless, Te Whatanui's people did not achieve total victory; both sides in the quarrel were considered winners and losers.
After this battle part of Ngati Raukawa occupied the Rangitikei district. Others retained Haowhenua and the Otaki district and Te Whatanui continued to live at Horowhenua. Tension eased, only to flare up again in 1839 at the battle known as Te Kuititanga. Ngati Raukawa attacked Te Ati Awa at Waikanae but were driven back.
There are few glimpses of Te Whatanui after Pakeha settlement began. He extended a welcome to missionaries, but used Henry Williams to carry messages to Mananui Te Heuheu, inviting him to attack Te Ati Awa. He sold land in Manawatu to the New Zealand Company, an action opposed by Te Rangihaeata. He spent much time laying down boundaries as Pakeha interest in the area increased. He was converted to Christianity by Octavius Hadfield, but remained convinced of the powers of tapu and makutu. By now he was an old man, and younger chiefs had moved to the fore. He may have spent his final years with relatives at Muhunoa, on the Ohau River. He died early in 1846. He was survived by his sons, Te Tutaki and Te Tahuri; his daughter, Rangingangana, had been married to Pomare II in peacemaking some years before.