Uenuku (or Uenuku-Kōpako, also given to some who are named after him) is an atua of rainbows and a prominent ancestor in Māori tradition. Māori believed that the rainbow's appearance represented an omen, and one kind of yearly offering made to him was that of the young leaves of the first planted kūmara crop. He was a tribal war god invoked before battles, particularly in the northern half of the country. It was said that if a taua appeared under the arch of the rainbow, it would be defeated in battle, and likewise, if they appeared to either side of the rainbow, they would be victorious. The Māori identified hawk feathers and a particular star called Uenuku as being sacred to him.

In Ngāti Porou and Ngāi Tahu stories, Uenuku was the Ariki of Hawaiki with 71 sons, all from different wives. In traditions from further north in the Pacific, Chief Uanuku Rakeiora and his son Ruatapu are said to have lived on Ra'iātea Island just over 27 generations ago, as descendants of Tangiia, contemporary of Iro-nui-ma-Oata (Whiro). The Aotea and Arawa tribes also have stories that relate to Chief Uenuku of Hawaiki.

In Ngāi Tūhoe stories concerning Uenuku's ascension to godhood, he betrays the trust of his supernatural wife, Hinepūkohurangi, and wanders the earth searching for her until he dies and transforms into a personification of the rainbow. The tribe claims descent from the union of Hinepūkohurangi and Te Maunga. The story is also known to Ngāpuhi, and to the Ngāti Kahungunu of Wairoa who claim descent from the union, where Hinepūkohurangi is known instead as Tairi-a-kohu. The tribes of the Kurahaupō canoe in Marlborough also regard him as an ancestor.

Uenuku is also particularly special to the Tainui Māori, who are said to have brought his spirit over from Hawaiki inside of a stone, and then transferred it into the carving of Te Uenuku. The Waikato Tainui used to invoke his spirit to temporarily inhabit smaller idols during times of war, which they would carry into battle to represent their guardian.

The first film Geoff Murphy directed was a freewheeling adaptation of the story of Uenuku and his lover, the mist maiden, in 1974. It was the first TV drama to be entirely performed in te reo (The Listener magazine softened viewers by providing a translation prior to screening).

According to the legends of the people of the Aotea canoe, Hoimatua sent his little son Potikiroroa to give part of a burnt offering to the ariki, Uenuku. Unfortunately, the poor boy tripped at the opening of Uenuku's house, Wharekura, which bothered Uenuku so much that he killed and cannibalized him raw.

During the next summer, Hoimatua's relative Turi slew Uenuku's son Hawepotiki in revenge. He and his friends then proceeded to eat of the body, and even managed to slip the child's heart into a food basket meant for Chief Uenuku. Uenuku lamented the absence of his son, not knowing where he was, and unwittingly bit into the heart. He was quickly informed of the deeds of Turi however, and calmly swore revenge, threatening that he would feed his son's murderers to Toi-te-huatahi. Turi's wife Rongorongo later overheard Uenuku chanting incantations of revenge, so he took his people and fled to New Zealand.

According to tradition, Uenuku was a descendant of Tūmatauenga and became angry when his wife, Takarita, committed adultery with two other men, so he killed all three of them. To add insult to injury, he cooked her heart and fed it to his son Ira. Her brother, Tawheta, was more than upset with this, and so gathered a group of men and ambushed five of Uenuku's sons. Maputukiterangi, Ropanui, Mahinaiteata, and Whiwhingaiterangi were killed. The fifth, Rongoruaroa, barely survived, but he was wounded. He dragged himself back to the pā of Uenuku, who had unwittingly been entertaining his enemies as guests the whole time. Upon learning of the attack, and with a sense of duty to being a hospitable host, he instructed the guests to leave, and warned that he would pursue them at a later date.