From a hobby in 2004 to over 1.8 billion monthly active users, here’s the story of Facebook.

While he was at Harvard, Mark Zuckerberg built websites as a hobby. He built Facemash, which allowed his classmates to rate students as attractive or not. He also helped friends with another site called HarvardConnection. His friends eventually sued Zuckerberg, claiming he stole their idea for the creation of Facebook.

The Facebook, as it was originally called, launched in January 2004 to Harvard students only. Four college roommates (Eduardo Saverin, Dustin Moskovitz, Andrew McCollum and Chris Hughes) joined Zuckerberg to help promote the site. Within two months it had expanded to three other universities and then eventually to most US and Canadian campuses.

By June 2004, Peter Thiel, the founder of PayPal had invested half a million dollars in exchange for just over 10% of the company. By the end of the year, they had over a million registered users. Zuckerberg didn’t plan to start a business, but by wanting to build the site, having it as a hobby and exciting people around him, it evolved into a company.

In September 2006, the site was opened to everyone and the site’s growth was boosted accordingly. In 2012, Facebook went public. After the stock market launch it was valued at $104 billion. It continues to be the most popular social networking site in the world and the company is now worth $350 billion.