A family fortune, beloved father and determination to overcome childhood infirmities set young Theodore Roosevelt on course to become the 26th president of the United States. Born into one of New York City’s wealthiest clans on October 27, 1858, Roosevelt was called “as sweet and pretty a young baby as I’ve ever seen” by his maternal grandmother, although his mother thought the newborn resembled a turtle.

Renowned for his vigor as president, Roosevelt possessed little of it as a child. Malnourished from a lack of appetite, the scrawny boy with a sunken chest  suffered from frequent colds, coughs, nausea, headaches, cramps and fevers. Let alone dream that their young “Teedie” could one day occupy the White House, Roosevelt’s parents feared he wouldn’t survive his fourth birthday.

Three-year-old Teedie suffered terrifying asthma attacks that struck without warning. Propped up in a bed or a chair, the fragile, frightened child felt as if he was drowning as he endured endless nights wheezing and gasping for air. “I was a sickly, delicate boy, suffered much from chronic asthma, and frequently had to be taken away on trips to find a place where I could breathe,” Roosevelt recalled in his autobiography.

Roosevelt’s parents tapped into their considerable coffers to care for Teedie—although many of the Victorian-era remedies proved medically dubious. Doctors administered electric shocks, controlled bloodletting and massages so rigorous they made the boy’s chest bleed. They prescribed black coffee, cigar smoking and even ipecac to induce vomiting in the belief that food placed undue pressure on his lungs.

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Ultimately, Roosevelt’s father proved the best tonic for the ailing boy, holding him in his arms and carrying him upright whenever he struggled for air. “I could breathe, I could sleep, when he had me in his arms,” Roosevelt recalled. The elder Roosevelt searched far and wide for fresh air that could fill his son’s lungs, taking Teedie on a year-long trip to Europe and on open-carriage rides up and down Broadway on frosty nights.

Theodore Roosevelt, Sr. also breathed a philanthropic spirit into his namesake. Teedie watched as his father, whom he regarded as “the ideal man,” donated his time and money to poorhouses and orphanages, helped found the New York Museum of Natural History and attended one, if not two, religious services each Sunday. After church every week, Teedie vied for his father’s approval by trying to outdo his siblings by memorizing two Bible verses and writing the best summary of that day’s sermon. “He could not yet be the strong and healthy son his father wanted, but Theodore had already learned that the road to his father’s favor was also paved with piety,” Kathleen Dalton, author of Theodore Roosevelt: A Strenuous Life, tells HISTORY.com.

Although lacking in physical strength, the wisp of a boy abounded in intellectual power. Often confined to bed, the curious Teedie was tutored at home and found companionship on the bookshelves of his family library. “As he gasped for breath, Roosevelt kept going by reading avidly—especially the adventures that featured struggle and triumph against danger by larger-than-life heroes,” Dalton says. “Already his imaginative life was peopled by the Ivanhoes, Robin Hoods, Natty Bumpos and Civil War and American Revolutionary soldiers, all heroic male adventurers who transported him far from his sickbed.”

While the asthmatic boy’s need for pure air sparked a lifelong affinity for outdoor spaces, the science books he devoured, including those penned by Charles Darwin, kindled his love of nature. Roosevelt amassed a collection of animal specimens and, to the consternation of the family’s housekeepers, took professional taxidermy lessons. His menagerie included snapping turtles and a family of gray squirrels. He kept live mice in his shirt drawer and dead ones in the icebox. By age 11, Teedie had collected 1,000 items that he referred to as the “Roosevelt Museum of Natural History.”

“He went to nature to learn scientific facts,” Dalton says, “because science was the new truth of his age, and it shaped his view of the world as much as any other set of ideas.”

As Teedie’s teen years approached, his father challenged the frail boy: “Theodore, you have the mind, but you have not the body, and without the help of the body the mind cannot go as far as it should. You must make your body.”

A human whirlwind for whom idleness was an enemy, Roosevelt threw himself into the drudgery of exercise to surmount his limitations. His father converted the second-story piazza of the family’s Manhattan brownstone into a makeshift gymnasium where Teedie poured hours into hanging from gymnastics rings and parallel bars. He took boxing lessons from a prizefighter and visited a nearby gymnasium every day to lift weights.

READ MORE: How Teddy Roosevelt Crafted a Vision of American Manliness

When 13-year-old Teedie received his first gun, the extremely nearsighted boy couldn’t shoot straight. After failing to even see the letters on a distant billboard that his friends were reading, Roosevelt received his first pair of glasses, which opened his eyes in more ways than one. “I had no idea how beautiful the world was until I got those spectacles,” Roosevelt later wrote.

Roosevelt’s asthma attacks never completely abated, but they did subside. Although they might have naturally ebbed as he grew toward adulthood, Roosevelt credited his vigorous exercise regimen, which bolstered his belief in the value of hard work. Having been taught that exercise and outdoor living built character—and having seen the impact they had on him—Roosevelt extolled “the doctrine of the strenuous life,” as he called it in an 1899 speech. “That highest form of success,” Roosevelt said, “comes not to the man who desires mere easy peace, but to the man who does not shrink from danger, from hardship or from bitter toil.

The incredibly prolific Roosevelt practiced what he preached. The once sickly boy graduated from Harvard University, authored more than 30 books, rose through the ranks of New York politics while enduring the deaths of his mother and first wife on the same day, became a war hero after organizing the Rough Riders and ultimately became the youngest president in American history. In doing so, he fulfilled the credo of his revered father: "Get action. Do things. Be sane. Don't fritter away your time."