Joseph-Augustin Chaho (Tardets 1811 – Bayonne 1858; name spelled Agosti Xaho in its Basque form) was a French-Basque journalist, writer and politician who has been considered both a radical forerunner of Basque separatism and a reactionary double-agent in the ranks of Spanish republicanism. A Freemason and myth-monger, Chaho invites such contradictions.

As a student in Paris, he became involved in various Romantic and “visionary” literary coteries such as the one around Charles Nodier, and published Paroles d’un voyant (1834) as a response to Lamennais’ Paroles d’un croyant. His first Basque-language publication was the rambling diatribe Azti-beguia (1836, “The eye of the seer”).

On his return to the Basque part of France, Chaho worked with various eminent regional personalities, such as D’Abbadie, with whose help he wrote Etudes grammaticales sur la langue euskarienne (1836), and the Vicomte Belzunce, with whom he wrote a Basque history (of their Histoire des Basques, Chaho wrote the first volume, on the Histoire primitive des Euskariens-Basques). In Bayonne he edited L’Ariel (1844), a controversial Republican-leaning newspaper, published a free-thinking Philosophie des religions comparées (1846) and a historical novel Lelo ou la Navarre il y a 500 ans (1848). He also began a political career as a republican in city politics and took a leading part in the revolution of 1848 as a city councillor. The Bonapartist backlash closed his newspaper and forced him into exile in Vitoria (Spain) for two years. Upon his return to France, Chaho withdrew from politics and began working on a quadrilingual Basque-French-Spanish-Latin dictionary, a first volume of which appeared in 1856. He died before completing it.

Although Chaho was a marginal and even eccentric figure, his writings had a major impact on Basque nationalism in Spain. In his best-known work, Voyage en Navarre pendant l’insurrection des Basques (1830-1835) (1836, based upon his own experiences in the First Carlist War), he saw the Carlist revolt as a struggle for ethnic self-determination. That view, which today has little credit among historians, became an article of faith among certain early-20th-century nationalists and continues to influence political discourse of the ETA terrorist group.

Chaho published collections of self-invented Basque legends, folk songs, proverbs and tales. His narrative Aitor, légende cantabre (1845) related a Basque origin myth around a hero-founder of the Basque race, Aitor; although wholly of Chaho’s fabrication, it was popularly accepted as a genuine tradition. This fiction became a point of reference, and Aitor became a powerful political symbol, for various schools and political currents in Basque letters. Also, in the dedication of his Etudes grammaticales sur la langue euskarienne (1836), he influentially coined the formula of Zazpiak Bat, “the seven are one”, to express the ethnic solidarity between the seven Basque provinces divided by the French-Spanish border.