Thanks to Issie Lapowsky and WIRED for this article. ON FEBRUARY 4, 2004, back when "Hey Ya!" was still topping the charts and global dominion was but a glimmer in a young Mark Zuckerberg’s eye, the 19-year-old Harvard sophomore and his roommates unleashed their creation, TheFacebook.com, on humanity. Or at least, they unleashed it on the elite sliver of humanity that occupies Harvard's halls. But over the past 15 years, that sliver has expanded far beyond anyone's expectations—including Zuckerberg's. In June 2004, when WIRED published its first story on TheFacebook, comparing it to Friendster and whatever the heck Orkut was, Zuckerberg said, "I expected that a few people would do it at Harvard and they'd tell their friends, but I didn't expect it would take hold as this all-inclusive directory."

At that point, success meant having 250,000 users on the platform. In the decade and a half since, Facebook has added four zeroes to that figure, transforming from a website for poking your college crush to, arguably, the most powerful engine of communication in the world. Zuckerberg's creation has, for better and for worse, forever changed how people connect, how businesses make money, how politicians seize power, and how information flows across communities and cultures. It's where grannies share pictures of their grandkids and where state-sponsored trolls wage cyberwar against other countries. It's how volunteers raise money for hurricane victims and how hate-mongers rally their followers to kill people.

How did that happen? We took a look back at Facebook's 15 years for the 15 moments that made the company what it is today and that signaled, sooner than most realized, what it would become.

1. The Winklevii sue Facebook.

TheFacebook.com was just seven months old when ConnectU, a startup founded by Harvard students Cameron and Tyler Winklevoss and Divya Narendra, sued Facebook for breach of contract in 2004. In what would become a years-long legal battle, memorialized in the Oscar-winning film The Social Network, the ConnectU founders alleged that Zuckerberg stole their idea and breached an oral contract he made to develop a social network for Harvard students that was then called HarvardConnection.

Zuckerberg had already launched a short-lived Hot or Not clone called FaceMash the year before. That site got him in trouble with Harvard, because the app used students' photos without their permission, but it also caught the attention of the HarvardConnection founders, who turned to Zuckerberg for help building their site. What they didn't know then—and what would later be revealed through court filings and leaked instant messages—was that, while Zuckerberg appeared to be toiling away on HarvardConnection, he was simultaneously building TheFacebook.

The HarvardConnection team sent Zuckerberg a cease and desist letter days after TheFacebook launched and filed a formal lawsuit that September.

The bitter suit ended in a settlement. But the battle with the Winklevii provided an early look at how Facebook would come to use a combination of skill, speed, and eventually, size to copy or crush competitors.