There were ideas long before there were light bulbs. But, of all the ideas that have ever turned into inventions, only the light bulb became a symbol of ideas. Earlier innovations had literalized the experience of “seeing the light,” but no one went around talking about torchlight moments or sketching candles into cartoon thought bubbles. What made the light bulb such an irresistible image for ideas was not just the invention but its inventor.

Thomas Edison was already well known by the time he perfected the long-burning incandescent light bulb, but he was photographed next to one of them so often that the public came to associate the bulbs with invention itself. That made sense, by a kind of transitive property of ingenuity: during his lifetime, Edison patented a record-setting one thousand and ninety-three different inventions. On a single day in 1888, he wrote down a hundred and twelve ideas; averaged across his adult life, he patented something roughly every eleven days. There was the light bulb and the phonograph, of course, but also the kinetoscope, the dictating machine, the alkaline battery, and the electric meter. Plus: a sap extractor, a talking doll, the world’s largest rock crusher, an electric pen, a fruit preserver, and a tornado-proof house.

Not all these inventions worked or made money. Edison never got anywhere with his ink for the blind, whatever that was meant to be; his concrete furniture, though durable, was doomed; and his failed innovations in mining lost him several fortunes. But he founded more than a hundred companies and employed thousands of assistants, engineers, machinists, and researchers. At the time of his death, according to one estimate, about fifteen billion dollars of the national economy derived from his inventions alone. His was a household name, not least because his name was in every household—plastered on the appliances, devices, and products that defined modernity for so many families.

Edison’s detractors insist that his greatest invention was his own fame, cultivated at the expense of collaborators and competitors alike. His defenders counter that his celebrity was commensurate with his brilliance. Even some of his admirers, though, have misunderstood his particular form of inventiveness, which was never about creating something out of nothing. The real nature of his genius is clarified in “Edison” (Random House), a new biography by Edmund Morris, a writer who famously struggled with just how inventive a biographer should be. Lauded for his trilogy of books about Theodore Roosevelt, Morris was scolded for his peculiar book about Ronald Reagan. Edison may have figured out how to illuminate the world, but Morris makes us wonder how best to illuminate a life.

Edison did not actually invent the light bulb, of course. People had been making wires incandesce since 1761, and plenty of other inventors had demonstrated and even patented various versions of incandescent lights by 1878, when Edison turned his attention to the problem of illumination. Edison’s gift, here and elsewhere, was not so much inventing as what he called perfecting—finding ways to make things better or cheaper or both. Edison did not look for problems in need of solutions; he looked for solutions in need of modification.

Born in 1847 in Ohio and raised in Michigan, Edison had been experimenting since childhood, when he built a chemistry laboratory in his family’s basement. That early endeavor only ever earned him the ire of his mother, who fretted about explosions, so, at thirteen, the young entrepreneur started selling snacks to passengers travelling on the local railroad line from Port Huron to Detroit. He also picked up copies of the Detroit Free Press to hawk on the way home. In 1862, after the Battle of Shiloh, he bought a thousand copies, knowing he would sell them all, and marked up the price more and more the farther he got down the line. While still in his teens, he bought a portable letterpress and started printing his own newspaper aboard the moving train, filling two sides of a broadsheet with local sundries. Its circulation rose to four hundred a week, and Edison took over much of the baggage car. He built a small chemistry laboratory there, too.

One day, Edison saw a stationmaster’s young son playing on the tracks and pulled the boy to safety before an oncoming train crushed him; as a reward, the father taught Edison Morse code and showed him how to operate the telegraph machines. This came in handy that summer, when Edison’s lab caused a fire and the conductor kicked him off the train. Forced out of newspapering, Edison spent the next few years as a telegrapher for Western Union and other companies, taking jobs wherever he could find them—Indiana, Ohio, Tennessee, Kentucky. He had time to experiment on the side, and he patented his first invention in 1869: an electric vote recorder that eliminated the need for roll call by instantly tallying votes. It worked so well that no legislative body wanted it, because it left no time for lobbying amid the yeas and nays.

That failure cured Edison of any interest in invention for invention’s sake: from then on, he cultivated a taste for the practical and the profitable. Although legislators did not want their votes counted faster, everyone else wanted everything else to move as quickly as possible. Financial companies, for instance, wanted their stock information immediately, and communication companies wanted to speed up their telegram service. Edison’s first lucrative products were a stock-ticker device and a quadruplex telegraph, capable of sending four messages at once. Armed with those inventions, he found financial support for his telegraphy research, and used money from Western Union to buy an abandoned building in New Jersey to serve as a workshop.

In 1875, having outgrown that site, he bought thirty acres not far from Newark and began converting the property into what he liked to call his Invention Factory. It was organized around a two-story laboratory, with chemistry experiments on the top floor and a machine shop below. Workshops are at least as old as Hephaestus, but Edison’s was the world’s first research-and-development facility—a model that would later be adopted by governments, universities, and rival corporations. Menlo Park, as it came to be known, was arguably Edison’s most significant invention, since it facilitated so many others, by allowing for the division of problems into discrete chemical, electrical, and physical components, which teams of workers could solve through theory and then experimentation before moving directly into production.

Menlo Park also included a three-story house for Edison’s family. In 1871, when he was twenty-four, he married a sixteen-year-old girl named Mary Stilwell, who had taken refuge in his office during a rainstorm. They had three children, two of whom Edison nicknamed Dot and Dash. It is likely thanks to them that the first audio recording ever made, in November of 1877, features Papa Edison reciting “Mary Had a Little Lamb.”

The phonograph came about because Edison had been experimenting with telephones, trying to improve on Alexander Graham Bell’s transmitter to achieve better sound quality across longer distances. He first had in mind a kind of answering machine that would transcribe the contents of a call, but he quickly realized that it might be possible to record the voice itself. To test the idea, Edison spoke into a diaphragm with a needle attached; as he spoke, the needle vibrated against a piece of paraffin paper, carving into it the ups and downs of the sound waves. To everyone’s surprise, the design worked: when he added a second needle to retrace the marks in the paper, the vibrating diaphragm reproduced Edison’s voice.