Duolingo is an American educational technology company founded in 2009 by Carnegie Mellon professor Luis von Ahn and his student Severin Hacker, who aimed to make education free and accessible after seeing the high cost of learning English in Guatemala. The platform offers courses in 42 languages—from common ones like Spanish and French to rare and constructed languages like Navajo, Hawaiian, and Klingon—along with lessons in music, math, and chess, all delivered through a gamified system of points, rewards, and short daily exercises. Operating on a freemium model, the app provides free ad-supported content while offering a paid subscription for an ad-free experience with extra features, plus separate products like the Duolingo English Test for certification and Duolingo ABC for children's literacy. The company grew rapidly, raising $3.3 million in its first funding round in 2011, launching publicly in 2012, and surpassing 200 million registered users by 2017 after a $25 million Series E round. A quirky detail: the iconic green owl mascot, Duo, exists because co-founder Hacker reportedly hates the color green, making it a memorable symbol of the brand's playful approach to learning.