Most people know Theodore Roosevelt as a former U.S. president. However, that was just a small part of what made the great man so unique.

“He grabbed life by the horns and took things on his own terms,” says Tom Hickey, owner of Hickey Custom Pools in Tucson, Ariz. “He was quite the adventurer.”

As a child, it seemed unlikely that Roosevelt would ever amount to much physically.

Born sickly, his early years were marred by illness and asthma so severe there were times when it seemed he might suffocate. But then his father took action.

Believing exercise would help, Roosevelt Sr. built a gym in the family home, and put his son on a strict workout regimen that would continue for the rest of Teddy’s life.

“Theodore, you have the mind, but you have not the body,” he said. “You must make your body. It is hard drudgery… but I know you will do it.”

He was right.

Roosevelt went on to claim second place at the Harvard boxing championships, and also took up wrestling and judo, earning a third-degree brown belt.

“He was really up against it physically,” Hickey says. “But instead of sitting back … he turned his whole constitution around. He turned into a robust character from a sickly kid.”

When Roosevelt was 25, a doctor advised him to find a desk job because of a serious heart condition. Instead, he set out for North Dakota to become a rancher.

He had mixed success tending cattle, but he embraced the hardships of life on the frontier. Roosevelt learned to ride long hours on horseback, cut down trees for firewood and hunt animals for food. He even became deputy sheriff of Billings County, taking on lawless vagabonds.

His adventuring spirit was put to the test in 1886 after four thieves stole his riverboat. With the help of two ranch managers, Roosevelt constructed a makeshift scow and took to the Little Missouri River to find the stolen boat.

After four days, they spotted the abandoned riverboat and hid in the brush until the thieves returned. Roosevelt captured the men and escorted them to Dickinson, N.D., to stand trial, going 40 straight hours without sleep to ensure no one escaped.

These types of frontier stories helped build Roosevelt’s reputation as a fearless cowboy, which later defined his campaigns for public office. However, his terms as New York governor and U.S. president hardly quelled his taste for adventure.

“He was able to live in both worlds, which is what makes him such an interesting person,” Hickey says. “He really liked getting out into the back country.”

After finishing his second term as president, Roosevelt journeyed to Africa for a 14-month hunting trip that stretched from Egypt to the Congo. Though he routinely hunted dangerous game, including lions and bull elephants, one encounter nearly proved fatal.

Hunting in the Central African savannah, Roosevelt and his guide approached a giant bull rhino. As Roosevelt lined up his rifle, the rhino spotted the two men and charged.

Roosevelt fired and hit the animal in its chest, but the rhino continued to speed toward them with blood visible in its nostrils. Just 13 steps away, both men fired again to finally bring the animal down.

“This was a wicked charge, for the rhino meant mischief and came on with the utmost determination,” Roosevelt later recalled.

In 1913, he again embarked on a daring expedition, this time to the rainforests of Brazil. The trip was supposed to be a traditional tour, but Roosevelt talked to the country’s foreign minister and settled on a more daring goal — to navigate the headwaters of the Rio da Duvida (River of Doubt) and trace it to its source.

Led by Brazilian explorer Candido Rondon, the group had to survive more than the elements. After he was caught stealing rations, a hired hand killed another member of the group and disappeared into the jungle. Effectively losing two men, the crew pushed on in the face of deadly rapids and dwindling supplies.

The hardships eventually would lead to Roosevelt’s undoing.

During the journey, he contracted malaria and lost 50 pounds. He also fell prey to a serious infection from a leg wound, which made traveling even more difficult. Roosevelt insisted the expedition continue, but complications from his illness would ultimately contribute to his death in 1919.