History.com: 6 Key Inventions by Thomas Edison

Edison's genius was improving on others' technologies and making them more practical for the general public. Thomas Edison applied for his first patent in 1868, when he was just 21 years old. The famous inventor's first brainchild was for a device that recorded legislative votes. That was just the start of a career in which he would obtain 1,093 U.S. patents, in addition to another 500 to 600 applications that he either didn't finish or were rejected. But Edison's greatest invention may have been developing a new process for coming up with inventions.