Born May 5, 1865, Mato Grosso, Brazil
Died January 19, 1958, Rio de Janeiro, Brazil

By the mid-nineteenth century Brazil’s Amazon River valley had become settled with plantations that produced rubber and other natural products. But there were still vast areas to the river’s south that had not been explored or developed, except for a few settlements along prominent rivers. Cândido Rondón, a Brazilian army engineer, was chosen by the government to help build a telegraph line across northwestern Brazil, through what would become the state of Mato Grosso into the Amazon valley. Between 1906 and 1909 he explored 193,000 square miles of little-known territory, charted the course of fifteen rivers, and discovered the River of Doubt (later renamed the Roosevelt River). In 1913–1914, he would return to map that river—accompanied by former U.S...