David Sacks was a founding COO at PayPal, so when it got acquired by eBay, he became a member of the PayPal Mafia — ex-PayPal employees who used their new money to invest in startups or launch their own, thus creating a whole new wave of tech.
Though Sacks went on to found Yammer and work as an interim CEO at Zenefits, he also used some of that cash to fund part of Uber's seed round.