For Andrew Carnegie, books were an indispensable tool for self-improvement and social uplift. Born poor in Scotland in 1835, the future industrialist immigrated to the United States as an adolescent and settled in Pennsylvania with his family. By age 13, he was already working 12-hour days, first as a bobbin boy in a textile mill and later as a messenger for a telegraph office. With no time to attend school, Carnegie was forced to educate himself by borrowing books from Colonel James Anderson, a wealthy local man who opened his private library to the community’s young workers. Carnegie would later credit Anderson’s free library with helping sharpen his mind and ease the drudgery of his work. “To him I owe a taste for literature which I would not exchange for all the millions that were ever amassed by man,” he wrote in his autobiography.

With the aid of the knowledge he gleaned from books, Carnegie later reached the pinnacle of success in the American business world. The former bobbin boy rose to become a personal secretary, railroad superintendent, financial investor and bridge company owner. By the 1870s, he had founded his first steel plant, which eventually grew into the mighty Carnegie Steel Company. In 1901, at the age of 65, Carnegie sold the business to industrialist J.P. Morgan for a cool $480 million—the equivalent of over $13 billion today.

The sale made Carnegie the richest man in the world, but the so-called “Prince of Steel” wasn’t content to sit idly and count his money. Saying that, “the man who dies rich dies disgraced,” he reinvented himself as a philanthropist and spent his later years using his fortune for the betterment of society. Carnegie funded retirement pensions for teachers, established the Carnegie Institute of Technology (later Carnegie-Mellon University), and set up scientific research centers and organizations devoted to world peace. He also furnished towns across the globe with everything from music halls and swimming pools to church organs.

Carnegie had started endowing libraries as early as the 1880s—the first was in his birthplace of Dunfermline, Scotland—but after selling his business he kicked the program into overdrive. From a few early locations in Pennsylvania, he eventually underwrote the construction of 2,811 libraries around the world. Carnegie considered free access to books to be a fundamental asset for immigrants and ambitious citizens looking to educate themselves, just as he once had with Colonel Anderson’s library. “It was from my own early experience that I decided there was no use to which money could be applied so productive…as the founding of a public library in a community which is willing to support it as a municipal institution,” he wrote.

Carnegie’s early libraries were mostly located in places where he had business interests or personal connections, but he eventually expanded his largesse to the majority of the English-speaking world. Nearly 1,700 of the libraries were located across the United States both in major cities and in tiny towns. There were Carnegie libraries in New York and Chicago, but also in more remote places such as Talladega, Alabama, and Thermopolis, Wyoming. There was even a lone branch in Hawaii. Several hundred other Carnegie libraries were erected in Canada, England, Scotland and Ireland. There were also scattered libraries in such far-flung places as the Caribbean, South Africa, Australia, New Zealand and even the Pacific Island of Fiji.

Over time, Carnegie developed a specialized process for funding his libraries. Communities looking for a grant simply wrote a letter to Carnegie and his personal secretary, James Bertram, in which they listed their population, their reasons for needing a library, and a strip of publicly owned land where it could be located. Carnegie would then provide money for the construction of the building itself—usually around $10,000—but he typically required the municipality to stock it with books. He also demanded that each recipient city pony up at least ten percent of his grant each year to fund the library’s employee salaries and operational costs, a practice that he believed kept communities invested in the building’s success.

While the libraries never had a set architectural style, Carnegie and Bertram eventually provided communities with a short booklet that included design templates. They also counseled that each building feature a small theater for lectures and educational programs. Carnegie didn’t require that the libraries be named after him—though many eventually were—but he sometimes requested that a rising sun and the words “Let There Be Light” be engraved near the entrance to symbolize the illuminating qualities of books and knowledge.

While Carnegie’s program constituted the largest individual investment in public libraries in American history, it was not without its critics. Some believed that former tycoon was trying to burnish his image after years of cutthroat business practices, and labor unions occasionally lobbied against his grants. “Carnegie ought to have distributed his money among his employees while he was making it,” a Detroit labor official named C.H. Johnson once quipped. Other towns rejected Carnegie’s charity out of personal pride. When he once offered to fund a new library in Louisville, Kentucky, the city’s Louisville Evening Post argued against accepting a donation from a wealthy benefactor. “Louisville is not a pauper city, and must not accept gifts from Princes not of her own people,” the article read. “Louisville is able and willing to maintain a library, but it will not build a monument to Mr. Carnegie.”

Several other towns balked at the cost of providing annual funding for their libraries, yet for every community that declined Carnegie’s money, many more accepted. During a period when books were often only available through subscription services, Carnegie’s grants led to an explosion of interest in free-to-all libraries, particularly in small towns in the Midwest. Indiana, for example, eventually received 156 Carnegie grants—more than any other state in the union.

By the end of his life, Carnegie could claim to be the primary financier of nearly half of all the public libraries in the United States. A few hundred of the buildings have since been demolished or destroyed by fires, but most are still standing, and as many as half continue to operate as libraries. Some of the most notable examples include the Detroit Public Library and the Carnegie Library of Pittsburgh.

All told, Andrew Carnegie eventually gave away roughly 90 percent of his personal fortune during his lifetime. Some $60 million—the modern equivalent of around $1.5 billion—went solely to the construction of libraries. By the time he died in 1919, the former “Prince of Steel” and captain of industry had earned himself a new nickname: the “Patron Saint of Libraries.”