Hirini (Sidney) Whaanga Christy, great-grandson of Ngāti Rakaipaaka and Ngāti Kahungunu leader Īhaka Whaanga, was born on 16 August 1883 at Nūhaka. His mother, Mihi Mere Whaanga, was the eldest daughter of Hirini Te Rito Whaanga and his third wife, Mere Hunonga Schmidt (Mete) of Ngāti Te Kauaha, a hapū of Ngāti Rakaipaaka of Nūhaka. Hirini's father was Hūpa Hēnare Christy, eldest son of Wiremu Kahukura Christy of Ngāti Rakaipaaka and his wife, Mere Harete (Hallett). Through his great-grandfather, Te Apatū-o-te-rangi, Hirini claimed descent from the ancestor Te Rauhina.
Hirini was adopted by his grandparents Hirini and Mere Whaanga. In 1894 he and other relatives went to Utah, where his grandparents worked in the Salt Lake Temple recording and affirming iwi genealogies. After arriving in Salt Lake City, the whānau was mistakenly thought to be a polygamous family. Since polygamy was no longer practised, this proved to be an embarrassment to those who were unaware of the extended family of the Māori. They were moved to Kanab, southern Utah, where misplaced trust and misguided speculation saw them lose most of their funds. Hirini, with other family members, found work on farms to help make ends meet. An ex-missionary, Benjamin Goddard, who knew the family and their position in Māori society, helped them to return to Salt Lake City. There Hirini attended school and later graduated from the Latter Day Saints University. He was well known as a star athlete at the university.
After his graduation, Christy worked at farming in Montana and gold prospecting in Nevada. He then travelled across the United States as tenor soloist in his cousin Walter Smith's 'Hawaiian Band'. Christy also sang in the Salt Lake Mormon Tabernacle Choir. On 16 January 1907, at Salt Lake City, he married Kathleen (Kate) Welsh, of Ngāpuhi and Irish descent who had been adopted by missionaries and taken to live in Salt Lake City. The couple had 14 children. They lived in Forest Dale with others of the whānau and Christy worked as a clerk.
In 1918 the family returned to settle in Nūhaka, where they served as leaders in Mormon church activities. Hirini Christy, the first Māori appointed to the church's Council of Seventy, served in the local, district and mission organisations. He made a living as a farmer, but was also heavily involved in the affairs of his people. He worked as an interpreter and adviser in the Native Land Court, was a member of the Tairāwhiti District Māori Land Board, and chaired or held membership in tribal, marae, and Māori land corporations. He assisted the preparation of claims and briefs for presentation in court. In 1936 he made an unsuccessful submission for the Ngāti Rakaipaaka people in their land claim against the Crown for part of the Nūhaka No 1 block; it was central to the claim later submitted to the Waitangi Tribunal.
On the outbreak of the Second World War, the Mormon missionaries were recalled to the United States. The task of sustaining the church in these years fell heavily on the people of Nūhaka, Māhia and Wairoa. Following the war, the church wished to show its recognition of their efforts. Hirini Christy and his close friend Apirana Ngata suggested that a carved meeting house be erected as a memorial to the district’s returned Māori servicemen; the church would provide funds to train them in Māori arts. The house, opened at Nūhaka in 1949, owed much to the respect and affection in which Hirini Christy was held.
From 1939 to 1945 Christy had chaired the Nūhaka branch of the Māori War Effort Organisation. In 1949 he chaired Turi Carroll's election campaign for the Western Māori seat on behalf of the New Zealand National Party. He was also a trustee on the Wairoa marae. Hirini Christy died at Wairoa on 1 July 1955. Kathleen had died in 1940, and he was survived by 11 of their children.