Year: 1999
Dorsey is a two-time college dropout. While at his first school, the University of Missouri-Rolla, he hacked into the website for a company called Dispatch Management Services and found a security flaw. The company's founder, Gregg Kidd, hired Dorsey immediately and convinced him to move to New York, where the offices were located.
Dorsey enrolled in NYU while there, but dropped out shortly after to move with Kidd to San Francisco. The two then launched a software company called dNet that provided same-day delivery for online purchases. They secured early funding from the investment group Band of Angels, but the company soon flopped. Dorsey wouldn't help create Twitter for another six years.
Source: WIRED, Vanity Fair