With his official duties completed two months after arriving in South America, Roosevelt was ready to begin his expedition. It would take at least two months to reach the River of Doubt. The grueling journey would take the expedition into areas of wilderness and danger. Only a handful of non-Indigenous men, led by Rondon, had ever reached the River of Doubt. That journey in 1909 had been brutal, with the men who survived left on the brink of starvation and “so weak that many of them could hardly crawl” (79).

Rondon was orphaned at an early age and raised by his grandparents in a remote part of Brazil. Despite his poverty, which led to his malnourishment in school, he earned a degree in mathematics and science and became a military engineer. As a positivist, Rondon trusted scientific observation over mysticism. Rondon cared passionately about the Indigenous peoples of South America and wanted to incorporate them into Brazilian society. He was selected to head the Strategic Telegraph Commission, which installed telegraph lines in the Amazon. It was brutal work and was how he had stumbled upon the River of Doubt.

Both Rondon and Roosevelt shared a tendency to thrive on physical hardship and overcome challenges with sheer force of will.