Maksymilian Rafailovych "Max" Levchin (Ukrainian: Максиміліан Рафаїлович Левчин; born July 11, 1975) is a Ukrainian-born American computer scientist. In 1998, soon after graduating from college, he co-founded (with Peter Thiel) the company that eventually became PayPal. Levchin notably made contributions to PayPal's anti-fraud efforts and is also the co-creator of the Gausebeck-Levchin test, one of the first commercial implementations of a CAPTCHA challenge response human test. He has also founded or co-founded the companies Slide.com, HVF and Affirm. He was an early investor in Yelp, an online social networking and review service, and was their largest shareholder as of 2012.