Alapaʻi (full name: Alapaʻinuiakauaua, known also as Alapaʻi I or Alapaʻi Nui, "Alapaʻi the Great") (died in 1754) was a king of Hawaiʻi island in ancient Hawaii. He was an usurper to the throne, but was considered a good ruler, one who loved the common people, although there is a story that he was responsible for the death of High Chief Keōua Nui.^[1] His title in Hawaiian was Aliʻi Aimoku.

Alapaʻi was a son of Kauaua-a-Mahi, son of Mahiolole, the great Kohala chief of the Mahi family, and Queen Kalanikauleleiaiwi. His brother was Haae-a-Mahi, and his half-siblings include Kekuiapoiwa I, wife of King Kekaulike of Maui, and Keeaumoku Nui, who were also his first-cousins by virtue of his mother's other marriages. The king of the island was Keaweʻīkekahialiʻiokamoku, his uncle. Alapaʻi ruled as the district chief of Kohala, subordinate to the King of Hawaiʻi.

After the death of his uncle and the subsequent civil war between his cousins Keeaumoku Nui and Kalaninuiamamao, Alapaʻi emerged as the victor and usurped the throne of Hawaiʻi. He reigned during one of the bloodiest period of Hawaiian history in an era of great warrior king fighting for the domination over the neighboring islands.

War continued between the century-old rivals Hawaiʻi and Maui during the early part of his rule while the old Kekaulike was still on the throne. After Kekaulike's death, his relations with Maui were friendly, and he helped his nephew Kamehamehanui Ailuau regain his throne from his half-brother Kauhiaimokuakama. His reign also saw a bitter conflict between Hawaiʻi and Oahu over the latters invasion of the island of Molokai, where Alapaʻi's relatives ruled. Alapaʻi killed Oʻahu's reigning king Kapiiohookalani at the Battle of Kawela and invaded the island of Oʻahu in 1736.

Kapiʻiohookalani's brother Peleʻioholani returned from Kauaʻi and repelled Alapaʻi's force, taking up the offenses on Maui and allying with Kauhiaimokuakama. The war eventually ended in a truce between Alapaʻi and Peleʻioholani, and Kauhiaimokuakama was drowned by Alapaʻi's orders.^[2][3]

When his niece Kekuʻiapoiwa was pregnant with Kamehameha, she had a craving for the eyeball of a shark, a sign that the child would be a killer of chiefs. Alapaʻi secretly made plans to have the newborn infant killed but was thwarted by the intervention Naeʻole who escaped with the child.^[4][5] He later reconciled with the baby and allowed it to be raised at his court placing him in the charge of his favorite wife Keaka.^[2]

Alapaʻi had many wives but only the names of three principal wives survived, and the name of one minor wife. His first wife was Keaka (sometimes called Keakakauhiwa); she belong to the Luahine family of Kohala which is said to be descended from Keakealanikane.^{[3] []} Their son was Keaweʻopala, who would succeed him.

His second wife was Kamakaimoku, his cousin, and their daughter was Manono I, grandmother of Keaoua Kekuaokalani.

His third wife was Kamaua with whom he had Kauwaʻa, a daughter, and Mahiua, a son. Kauwaʻa and her husband Nahili had two daughters: Julia Alapai, the wife of Keoni Ana, and Kaulunae, who married Kanehiwa and was the mother of Lipoa, a son, and Julia Moemalie, a daughter.^{[3] []}

He was also married to ʻUmiaemoku (born in 1788) and she bore him Keawemahi.^[6] Stepdaughter of Alapaʻinui was Queen Kānekapōlei.

Duke Kahanamoku was also a descendant through his paternal grandmother Kaoeha, a granddaughter of Makue and Halapu.^[7]

After his death in 1754, Alapaʻi was initially succeeded by his son, Keaweʻopala however, he would eventually be overthrown by Kalaniʻōpuʻu.^[2]