The Itsekiri (Iwere) kingdom was founded c.1480 by Prince Ginuwa, a son of Oba Olua of Benin, who left Benin City with seventy attendants — chiefs, slaves, drummers and the famous Ojoye nobility — and settled at Ode-Itsekiri (Big Warri) on the creeks of the western Niger Delta in present-day Delta State. Ginuwa took the title Olu (king); his successors continue to bear it. The Itsekiri language is a Yoruboid tongue carrying heavy Edo influence — a linguistic fossil of the kingdom's mixed Benin and Yoruba origins on a substrate of indigenous Ijo-related populations.
The Portuguese reached Warri in 1485. Augustinian missionaries arrived in the 1570s; in 1597 Olu Atorongboye sent his son and heir, Prince Domingos, to Portugal for education. Domingos studied at the Augustinian convent at Coimbra and at Lisbon, returned to Warri after roughly a decade with a Portuguese wife, Doña Maria, who survived him as queen regent, and reigned as Olu Sebastian. A Catholic chapel was maintained at Warri continuously from c.1620 until the late 18th century; Olu after Olu was baptised; the Pope appointed a titular Bishop of Warri. This makes Warri one of the earliest sustained African Catholic kingdoms — pre-dating the better-known case of Kongo by little, and exceeding it in royal-house continuity.
Warri's commercial role was as a middleman in the European slave trade and in the salt-and-fish trade with the Edo hinterland and the western Igbo. The kingdom never developed the canoe-house plutocracy of Bonny; the Olu remained the apex of a relatively centralised noble system (Ologbotsere, Iyatsere, Uwangue and Otonigwa palace chiefs).
The stool was vacant from 1848 to 1936 in a long dynastic dispute. The British Colonial Government acknowledged the restoration of the Olu in 1936 — Olu Ginuwa II — but the colonial wording of the gazette ('Olu of the Itsekiri', not 'Olu of Warri') has been the subject of communal litigation for ninety years among the Itsekiri, Ijaw and Urhobo communities of Warri. The Warri Crisis of 1997–2003, in which the contested status of the Olu and the Ijaw Egbema and Gbaramatu clans' demand for separate Bolowou kingship led to fighting on the creeks, killed several hundred people. The Olu of Warri is today HRM Ogiame Atuwatse III, installed 21 August 2021.