November 14, 1904: King C Gillette patented the Gillette razor blade. This disposable razor was the first safe alternative to the straight razor, which usually required visiting a barber. By selling the replaceable razor blade along with the permanent handle, King established a successful business model still used in razor sales today. King founded the American Safety Razor Company, later renamed the Gillette Company. This firm was purchased by the Proctor & Gamble Company in 2005.
You can view an image of the patent at the U.S. Patent and Trademark Office, search for number 775,134
50 Inventions That Shaped the Modern Economy, by Tim Harford T15 .H343 2017