10 of History's Happiest Accidents

The accidental discovery of Viagra's power to cure ED has made a lot of men very happy. Christopher Furlong/Getty Images

Until medical science invents a pill that makes men smarter, more attractive and filthy rich, Viagra will remain man's little blue best friend. Released to rave reviews in 1998, Viagra is still a huge moneymaker for drugmaker Pfizer, which reported more than $2 billion in sales in 2012 alone [source: Thomas].

Incredibly, Pfizer never set out to cure erectile dysfunction (ED). The invention of Viagra was a miraculous accident. Pfizer researchers were testing batches of a new angina (chest pain) medicine called UK-92480when subjects began reporting some unusual, er, stiffness. Further testing revealed that UK-92480 inhibited the production of an enzyme that undermined erections [source: British Pregnancy Advisory Service]. Renamed Viagra, the revolutionary ED pill became the fastest-selling drug of all time and made a lot of men a whole lot happier [source: Jay].