Traveling to the Amazon for the first time, in 1978, as a fledgling correspondent for Newsweek, was the fulfillment of a childhood ambition. I didn’t know what to expect. My first destination was a remote and rugged corner of northwestern Brazil called Rondônia, an area larger than Great Britain that, in those days, had only hundreds of thousands of residents scattered across makeshift settlements along riverbanks and small homesteads in the jungle. The military dictatorship that ruled Brazil had just built the 2,500-mile-long Trans-Amazon Highway in order to provide “land without men for men without land.” My assignment was to report on the road’s impact on the world’s largest tropical rain forest and its human population.

I knew that Rôndonia was named for Cândido Mariano da Silva Rondon, the Brazilian general who, in the first few years of the 20th century, had overseen construction of a telegraph line across more than 1,000 miles of hostile terrain. That’s all that I knew about him. As I roamed the territory bearing his name, my admiration grew. The heat was oppressive, the fear of tropical diseases such as malaria omnipresent, the food abysmal, the roads mostly notional, and the menace of wasps, ants, chiggers, mosquitoes, spiders, and poisonous centipedes never-ending.

One scorching afternoon, dripping in sweat and trying to fend off the stingless Amazon bees that always seemed to go straight for my eyes, ears, and nose, I had a sudden realization: This is just a small taste of what Rondon had to endure for months on end, year after year. He did it all a century ago, when conditions were infinitely more primitive. What kind of tough-as-nails badass must this guy have been?

Looking back, that moment probably marked the genesis of my new book, Into the Amazon. When I returned to my home base, in Rio de Janeiro, I sought out all the information about Rondon that I could find. What I discovered fascinated me. He was primarily of Indigenous descent, grew up as an orphan on the southern edge of the Amazon, stood a mere five feet three inches tall, weighed barely 100 pounds, and shepherded Theodore Roosevelt across the Amazon in a notoriously difficult expedition in 1914—only to have Roosevelt receive all the credit for their feats.

The heat was oppressive, the fear of tropical diseases such as malaria omnipresent, the food abysmal, and the roads mostly notional.

Not only that. Rondon turned out to be a distinguished scientist, the author of numerous papers about astronomy, anthropology, ethnography, and linguistics, as well as the largest donor of specimens to Brazil’s National Museum. He was the father of Brazil’s environmental movement, a pacifist, and a human-rights advocate who worked tirelessly to protect Brazil’s Indigenous peoples from the ranchers, miners, rubber tappers, and loggers encroaching on their land. On his own expeditions, he established peaceful contact with dozens of tribes, adhering to the motto “Die if you must, but kill never,” even when struck by arrows.

The idea of a “pacifist general” seemed astonishing to me. I was not the only one with that reaction. Rondon was nominated three times for the Nobel Peace Prize, the first time in 1925 by Albert Einstein, who while on a lecture tour of Brazil saw films of Rondon working in the field “without the use of weapons or coercion” and lauded him as “a philanthropist and leader of the first order.” When Rondon died, in 1958 at 92, the International Red Cross hailed him as the world’s leading exponent of nonviolence, after Gandhi. Calling him “pure, upright and without blood on his hands,” the French poet Paul Claudel, his good friend, went so far as to say that Rondon “conveys the impression of a figure from the Gospels.”

Rondon also had flaws and contradictions, which I eventually unearthed, too. With complete access to Brazilian government archives, I found that the avatar of nonviolence was court-martialed early in his career for whipping a disobedient soldier under his command. It was difficult to reconcile the accomplished scientist with his teenage self, a follower of the French philosopher Auguste Comte. Rondon never abandoned Comte’s creed of positivism, a mystical hodgepodge of religion and sociology which considered Aristotle, Shakespeare, and Descartes to be saints.

But when I look at Rondon now, having excavated his long and remarkable life, what I see most of all is a man who embodies the best of both modern and old-fashioned virtues. He was genuinely patriotic and adhered to traditional codes of honor, chivalry, and bravery. At the same time, his espousal of tolerance and cultural diversity, his recognition of the innate dignity of all human life, and his respect for the natural world and its eco-systems make him a very contemporary figure. With threats to the Amazon and its inhabitants now at existential levels, that makes Rondon more relevant than ever, and not just in Brazil.

Larry Rohter’s Into the Amazon: The Life of Cândido Rondon, the Blazing Explorer, Scientist, Statesman, and Conservationist is out now from W. W. Norton