A millionaire at just 28, Musk used money from the sale of Zip2 to found X.com, one of the world's first online banks, in 1999. The service enabled a variety of financial tools, including payment without a credit card.
Because X.com was perceived by some as an adult-themed website, Musk changed the name of this company to PayPal.com after it merged with rival Confinity. The new company doubled down on offering money transfer services via email and the web, and the business grew [source: Klebnikov].
But during a disagreement over the technical aspects of PayPal (he wanted to move the service to Windows from Linux), Musk was forced out of his position as CEO. He did remain on the board, however, so when eBay bought PayPal in 2002 (over his objections) for a whopping $1.5 billion in stock, he landed a windfall of about $160 million after taxes [sources: Kane, Klebnikov].
Interestingly, many of the people who worked at PayPal in its early days went on to found other giants of the internet economy, including Yelp, LinkedIn, YouTube and Square — so much so, that the group is often referred to as the "PayPal Mafia" [source: Parrish].