On February 4, 2004, a Harvard sophomore named Mark Zuckerberg launches The Facebook, a social media website he had built in order to connect Harvard students with one another. By the next day, over a thousand people had registered, and that was only the beginning. Now known simply as Facebook, the site quickly ballooned into one of the most significant social media companies in history. Today, Facebook is one of the most valuable companies in the world, with over 2 billion monthly active users.
The origins of Facebook have been highly scrutinized (including in the critically acclaimed 2010 film The Social Network), but the exact source of the idea remains unclear. What is obvious is that Zuckerberg had twin gifts for coding and causing a stir, both of which served him well at Harvard. The previous year, he had become a campus celebrity by creating FaceMash, a website where students could vote on which of two randomly-selected Harvard women was more attractive, and quickly running afoul of both the administration and several women's groups. FaceMash was short-lived but popular, leading Zuckerberg to consider the value of creating a campus-wide social network.
Over the course of his sophomore year, Zuckerberg built what would become Facebook. When it launched on February 4, he and his roommates were glued to their screens, watching as an estimated 1,200-1,500 of their fellow students signed up for their site within its first 24 hours of existence. From there, Facebook expanded rapidly, moving to other Boston-area schools and the rest of the Ivy League that spring. By the end of the year, the site had 1 million users, angel investor Peter Thiel had invested $500,000, and Zuckerberg had left Harvard to run Facebook from its new headquarters in California.
From there, Facebook spread across the world, becoming not only an incredibly valuable company but also one of the most important institutions of the early 21st century. The go-to social media site for a generation of internet users (and one which was readily adopted by older users as it transformed from exclusive to universal), Facebook was one of the major forces that brought the internet into the highly-participatory phase full of user-generated content sometimes referred to as "Web 2.0." It has also remained controversial. In addition to allowing misinformation and fake accounts to proliferate, Facebook has drawn criticism both for selling its users' data and for failing to adequately protect it. Nonetheless, Facebook continues to dominate the social media market, generating by far the most ad revenue and maintaining over half of the total market share.