“A diamond is forever” was named by Advertising Age the greatest advertising slogan of the twentieth century. It was written by a female copywriter named Frances Gerety in 1947. Gerety wrote all of De Beers’ ads for 25 years, and those ads changed Americans’ perception of diamonds and nudged them into equating the gem with love and marriage (which was not the case 75 years ago). An interesting New York Times profile of that early ad woman and her classic advertising slogan is here. Another entertaining story, from Adweek, is here.