Ask Luis Von Ahn why he decided to become an entrepreneur and he will tell you that the career actually chose him. When he was a professor at Carnegie Mellon in 2005, he developed a program that websites could use to distinguish humans from robots. CAPTCHA became so popular that school officials urged Von Ahn to turn the program into something more.
"At some point the university was kicking the project out because it had too many users and they just said, 'You can't be in the university, you have to do something about it,'" he says. "I had to turn it into a company."
In 2006, he received a prestigious six-figure MacArthur Fellowship, otherwise known as the "Genius Grant," which also recognized his work with CAPTCHA. In 2011, when, the entrepreneur estimates, his CAPTCHA system was digitizing two-and-a-half million books a year, he launched his new initiative, the free tool for language learners, Duolingo.
Though he never planned for entrepreneurship to be his career path, Von Ahn does appreciate the fortuity. He came from a family of business people. In Guatemala, his parents owned one of the largest candy producers in the country, Tropical Candy.
Today, there are 1.2 billion people around the world learning a new language. 150 million of them, aged seven to 95, are now using Von Ahn's website Duolingo to do that learning for free.
But reaching this milestone has been no easy feat. Here are some of the challenges Von Ahn has needed to overcome.