Korokī Te Rata Mahuta Tāwhiao Pōtatau Te Wherowhero was the elder of two sons of Te Rata, the fourth Māori King, of Ngāti Mahuta. His mother was Te Uranga of Ngāti Korokī and he was named for the eponymous ancestor of her people. He was born at Waahi, probably in 1908 or 1909. In his youth, Korokī, shy and reserved, was eclipsed by his younger brother, Taipū. Great things were expected of Taipū, who was sent to Wesley College in Auckland, but he died shortly after his arrival. Records show that Korokī attended Huntly School only briefly, in 1915. Alex McKay claimed that he taught Korokī to read and write in Māori in 1937, and he also attended Maharaia Winiata's adult education programme. Korokī himself felt ill-prepared for the kingship, and ensured a good education for his successors. Later in life he was to spend much time reading, in both Māori and English.
As a youth Korokī showed aptitude as a motor mechanic, and had he not been destined for the kingship would have chosen this line of work as a career. He was a good musician, playing in a band, and a keen footballer. Probably in the 1920s he developed a relationship with Te Paea Raihe; they had one daughter. About 1930 Te Puea Hērangi arranged a marriage for him with Te Atairangikaahu, daughter of Te Puea's brother Wanakore Hērangi. Their daughter, Piki, later to take her mother's name, was born in July 1931. They adopted a son, Robert Te Kotahi Mahuta, in 1939. Korokī and his family lived at Waahi pā, near Huntly.
Korokī's father, Te Rata, died on 1 October 1933. Korokī begged Te Puea not to make him take his father's place: he did not feel fit for the task, and the people were so poor they could not afford to support a king. He expressed similar doubts to Pei Te Hurinui Jones. But at the tangihanga for Te Rata it was agreed by all the visiting chiefs that the Kīngitanga should continue and that Korokī should be the successor. Apirana Ngata, Pei Te Hurinui and others encouraged Korokī to accept the kingship as a symbol of the mana of the Māori people. Pei Te Hurinui assured the young king of his personal support. This was the commencement of Pei Te Hurinui's career as one of the chief confidants and supporters of Korokī. Another was to be Piri (Bill) Poutapu, the well-known carver, who later acted as Korokī's secretary.
Korokī was crowned on 8 October 1933, which was also the day of his father's funeral. Te Puea bought him clothes to fit him for his new office, paid his father's few domestic debts and banked £100 to give him a good start.
In his first few years as King, Korokī, sometimes referred to as the 'boy' by his elder relatives, was closely supervised by his uncles Tūmate and Tonga Mahuta, and by the senior elder of the family, Haunui Tāwhiao. Tūmate and Tonga had their own plans for the kingdom, which they felt should retain its centre at Waahi pā. Haunui Tāwhiao was a follower of T. W. Rātana, and with Te Puea's cousin, Piupiu Te Wherowhero, succeeded in getting Korokī's first official act as King to be a visit to Rātana pā. Te Puea was doing her utmost to draw Korokī away from the Rātana movement and into her plans for the revival of the kingdom and the marae at Ngāruawāhia. Another faction was led by Tarapīpipi Taingākawa Te Waharoa at Rukumoana, Morrinsville, a centre also of Ngāti Hauā. The third kingmaker, he also claimed as a hereditary position the title tumuaki (leader) of the Māori Kingdom of Aotearoa and Te Waipounamu (the North and South Islands).
It was decided by the kāhui ariki (royal family) that Korokī must remain aloof from politics, yet every political action had to be done in his name, and his agreement, or at least his presence, obtained as an endorsement of their activities. Especially in his early years as King, he found himself pulled this way and that by the different requirements of his elders. At an early coronation hui at Waahi pā, an annual event throughout Korokī's reign, Haunui Tāwhiao had decided Korokī was not to appear on the marae; Te Puea told Korokī: ‘If there were no people there would be no need for a King! The people are here to honour you. You in return must honour the people'. Korokī went onto the marae.
Korokī's difficulties were apparent in his belated support for Tūmate in his negotiations for a settlement of the Waikato confiscation claim in 1938. He was committed to the support of Tūmate, but at the same time he was bound by his predecessors' recognition of the tumuaki and his Kauhanganui (Great Council) at Rukumoana. The tumuaki could use Korokī's presence at Rukumoana as an endorsement of his own more conservative position.
From the beginning of his reign Korokī's life was a round of official engagements. At Tūrangawaewae he entertained visiting VIPs, Polynesian royalty and nobility, governors general, prime ministers and ministers of the Crown, and Allied officers in the Second World War. He attended numerous poukai (meetings on Kīngitanga marae, where he renewed acquaintance with his people and received their contributions to the King movement). He also attended the tangihanga of many Waikato and Ngāti Maniapoto elders, and was a guest at many events in other tribal areas. He was at the Waitangi Treaty House celebration in 1934. The cost of these functions and visits was very high, and Korokī was often embarrassed by shortage of funds.
Not all of these occasions went off harmoniously, and Korokī's elders often refused to permit him to attend others. In Ōtaki, there was a controversy over whether it was fitting for Korokī to pass under a door lintel carved in the likeness of a female ancestor with her thighs open and sexual organs exposed. Ngāti Raukawa and Waikato elders with him were adamantly opposed. However, the carvers threatened all comers with the consequences of a breach of tapu if the carving was removed or altered. One version of the outcome was that Korokī entered by the window at the back of the house. In another, it was realised that he was a descendant of the female ancestor concerned, so that passing under the lintel would not demean him. Korokī turned down an invitation to the East Coast to attend the opening of Wī Pōtae's new house at Tokomaru in 1934 and one at Ōhinemutu in 1942. On both occasions, others had been asked to open the houses.
Many of the controversies in Korokī's reign related to the constant battle to maintain the dignity of the Kīngitanga and obtain both Pākehā and Māori recognition of it. It was a see-saw process, his special status alternately recognised and rejected. In 1933 Labour members of Parliament, grateful for the care shown to Harry Holland after his collapse at the graveside of Te Rata, sent an address to ‘King Korokī'. The governor general, Lord Bledisloe, paid Korokī special honour at Waitangi, and told him that he wanted him to be a figurehead for his people. But Ngata and other Māori were at pains to stress that they did not mind what the Waikato people chose to call their hereditary ariki, as long as he did not challenge the sovereignty of the British Crown and the New Zealand Parliament. In 1939 the government refused to exempt Korokī and his wife from registering under the social security regulations, and in 1946 Prime Minister Peter Fraser stated that Korokī could not be represented at international bodies such as the United Nations.
Korokī's status and financial support for his role as King were key elements in the negotiations in the 1930s and 1940s for compensation for the confiscation of Waikato lands in the 1860s. An appeal for statutory recognition of Korokī’s position was made in 1946, but Fraser said that he had no evidence that tribal groups outside Waikato supported such a demand. Following the establishment of the Tainui Māori Trust Board in 1946, grants were made to Korokī to cover the cost of Kīngitanga functions.
In 1948 there was pressure for a referendum on the sale of liquor in the King Country. A verbal promise had been made to Ngāti Maniapoto in 1885 by Premier Robert Stout, whereby liquor was banned from the King Country in return for its being opened to the railway and other developments. Korokī tended to favour the counter-proposal of Pei Te Hurinui that tribal welfare trusts in the King Country should benefit if licences were granted, but agreed to lead a delegation to demand the continuance of the pact. On 30 March 1949 Korokī and 600 supporters presented Fraser with a petition demanding the maintenance of the pact; they were met with courtesy and cups of tea, but by 1954 the King Country was ‘wet'.
On several occasions Korokī and his family refused to take part in receptions for British royalty at Rotorua. Te Puea explained to Eric Ramsden that it was her people's custom to receive important people on their own marae; they did not go to other marae to welcome them. This was the attitude taken in 1953 when an invitation to visit Tūrangawaewae, first extended by Te Puea in 1952, was again tendered to Queen Elizabeth II. After difficult negotiations, some at the last minute, a short visit took place on 30 December 1953. Korokī had wanted to present the Queen with a loyal address prepared by Pei Te Hurinui, but this was not permitted. However, a signed and sealed copy was later forwarded. In this document, for the first time, a Māori King swore allegiance to the British Crown.
After the earlier deaths of his uncles and, in 1952, of Te Puea, Korokī, at the instigation of the elders, commuted from Waahi pā to take up daily residence in Tūrongo House, Ngāruawāhia. From the late 1950s his health began to deteriorate, and although he continued to keep himself informed, and his opinion continued to be sought, he gradually dropped out of public life. He was represented by Pei Te Hurinui, his wife, Te Atairangikaahu, and his secretary, Piri Poutapu, among others, and increasingly in the 1960s his designated heir, Piki, took a prominent role. He died at Ngāruawāhia on 18 May 1966. Piki was crowned as Te Arikinui Te Atairangikaahu a few hours before Korokī’s burial on Taupiri on 23 May 1966.