King Gillette (I'm not making up his name) wrote an essay in 1894 on social reform entitled "The Human Drift" that was a complete and utter failure. So he decided to make money doing something else.
At the time razors need to be taken to a barber or cutler each time they needed sharpening. The idea came to Gillette that the world needed something better. He collaborated with an MIT professor named William Nickerson (once again, I'm not making up the name, but that one is strangely appropriate, isn't it?) In 1903 the first safety razors were introduced at five dollars a piece. In 1906 300,000 razors were sold. When America entered WWI, the government placed an order for 3.5 million razors to keep the army clean-shaven. Fortunes had been made.

I wonder if the safety razor would have been invented sooner if women shaving their legs had been a more common occurance.