Brazilian author of the classic historical narrative Os sertões (1902; Rebellion in the Backlands), the first written protest in behalf of the forgotten inhabitants of Brazil's frontier.

Originally a military engineer, Cunha left the army to become a civil engineer and later a journalist. As a reporter in 1896–97, he accompanied the army to Canudos, a village in the backlands of Bahia state, where the messianic Antônio Conselheiro (“the Counselor”) and his followers had established their own “empire.” Five successive government expeditions were required to subdue the rebels, who resisted to the last man. Cunha's eyewitness account of the drama of rebellion and reprisal has the vividness of a novel. With insights he developed as an amateur geographer and geologist and as a keen social observer, Cunha perceived not only the particular event but the larger significance of the inhospitable backlands and its inhabitants in the national life. In defiance of the common 19th-century pseudoscientific belief in the inferiority of mixed races (a theme that haunts Brazilian literature), Cunha concludes with a strongly worded plea that the republic commit itself to assimilating its caboclos (people of mixed European and Indian ancestry) into the mainstream of Brazilian life.

Cunha died tragically, shot in a personal quarrel. Every August Brazilians observe a Semana Euclideana (“Euclides Week”) in his honour.