Theodore "Teddy" Roosevelt served as president for two terms between 1901 and 1909. Growing up wealthy, but asthmatic, left him plenty of time to study nature and natural history. He eventually overcame his asthma and became a renowned sportsman, hunter, and boxer. He earned accolades on the battlefield during his time as a soldier, and when President William McKinley was assassinated in 1901, he became president at 42 — the youngest person to serve as U.S. president. Roosevelt created the first National Bird Preserve at Pelican Island, Fla., established the U.S. Forest Service, and created more than 190 million acres of new national forests, parks, and monuments. Besides being one of greenest presidents, Roosevelt was arguably the toughest — after he was shot by a would-be assassin, he surmised that the bullet didn't penetrate his lung and went on to give his speech, with blood spreading over his shirt. He went to the hospital only after collapsing.