Theodore Roosevelt was President of the United States from 1901 to 1909. Roosevelt was a renowned adventurer, and visited Amazonia in 1913 and 1914. A new river was discovered on one of these expeditions, and was named in his honor Rio Roosevelt.

Theodore Roosevelt, 26th President of the United States (1901-09). The son of a wealthy, socially prominent merchant, Roosevelt was born in New York City on October 27, 1858. After his father's sudden death in 1878, Roosevelt forsook scientific ambitions, developed political interests, and became engaged to Alice Lee of Boston, whom he married in 1880. Alice Roosevelt died in 1884, just after the birth of their only child. Their daughter, also named Alice, as Alice Roosevelt Longworth became a well-known Washington personality in later years. In 1886 Roosevelt married Edith Carow of New York, who became his most valued adviser. They had a daughter and four sons, the oldest of whom, Theodore Roosevelt, Jr., was a decorated hero in the two world wars.

His four sons all fought in World War I, and the death of the youngest, Quentin, in combat as an aviator in August 1918, was a heavy blow. Roosevelt's health deteriorated during the final years of his life, partly as a result of tropical fevers contracted on an expedition to the Amazon region of Brazil in 1913 and 1914 where he was guided by the famous Brazilian leader, Candido Rondon. The expedition concentrated around an area known the Rio do Dúvida (River of Doubt) – which was given this name because no one knew the river's route. Although people knew that the river flowed into another river called the Madeira, no one knew where. Roosevelt's expedition helped clarify this issue, and the river was renamed Rio Roosevelt in his honour.

Roosevelt was astonished that, in the Twentieth Century, it was still possible for a large river to have a course that was unknown. He died at his home in Oyster Bay, New York, on January 6, 1919