Incorporated into the lore but not the company's official bio is Facebook's beginning as Facemash, Mark Zuckerberg's collegiate version of Hot or Not. Zuckerberg faced disciplinary action after taking photos from the online facebooks of Harvard students and pitting them against each other, two at a time. In an email to The Harvard Crimson after he took down the site, Zuckerberg said, "Issues about violating people's privacy don't seem to be surmountable. I'm not willing to risk insulting anyone."

PayPal founder Peter Thiel was Facebook's first investor, handing over $500,000 to college sophomore Zuckerberg & Co. To encourage other students to swap their educational pursuits (at least temporarily) for tech dreams, Thiel has founded the Thiel Fellowship, which grants $100,000 to entrepreneurs under age 20 to take two years out of their schooling to build a startup.

Facebook was originally Thefacebook.com since Facebook.com was already taken. After a second round of funding netted it $12.7 million from Accel Partners, the company paid $200,000 for its desired domain and officially changed its name.

Facebook has seen its share of lawsuits over the years. From Harvard classmates who felt their idea was stolen (the Winklevoss twins, Divya Narendra, Aaron Greenspan) to some legal back and forth with co-founder Eduardo Saverin. There's also businessman Paul Ceglia, who has pursued a case for the past two years in which he claims Zuckerberg, whom he employed to help with his website StreetFax, granted him majority ownership in the company. Then there's the former Rotem Guez, who legally changed his name to Mark Zuckerberg, and is being sued by Facebook for violating its terms of service by selling Likes for Pages.

As of January 2012, Facebook has more than 800 million active users (about 80 percent of which are outside the United States), more than half of whom log on to the site in any given day. The average user has 130 friends and is connected to 80 community pages, groups, and events.

From the original four (Zuckerberg and Harvard classmates Chris Hughes, Dustin Moskovitz, and Eduardo Saverin), Facebook has grown to more than 3,000 employees in 12 cities in the United States and 14 cities abroad. Nearly three times more employees leave Google for Facebook than vice versa, based on LinkedIn stats. Though—here an employee, there an employee—it's lost a few to FarmVille-maker Zynga.

The pinnacle of Mark Zuckerberg's concept of frictionless sharing is the latest iteration of Facebook in which Actions are included on users' Timelines, reporting on everything from what news stories users are reading to the music they're listening to and what they just bought. It's similar to the much-condemned and now-defunct Beacon. Privacy issues have plagued the company since the beginning, with the FTC even getting involved; Facebook has agreed to 20 years of privacy audits by an outside monitor.

Zuckerberg has been portrayed by Jesse Eisenberg, parodied by Andy Samberg, presented with a Medal of Fear by Stephen Colbert, and pilloried for his style. A pre-IPO estimated net worth of $17.5 billion might cushion the blows, though. Not to mention that, according to Glassdoor, 93 percent of his employees approve of the job he's doing. And he's earned karma, not just cash, having signed the Giving Pledge, a billionaire's oath promoted by Bill Gates and Warren Buffett, to donate at least half of his wealth to charity.

Friendster and MySpace were long ago mowed down, clearing a path for Facebook. Google+ is now its only true competitor, with 90 million users (though that number is in dispute). Microsoft, Google's search rival, paid $240 million for a 1.6 percent share of Facebook in 2007. The bond between the companies goes even deeper, with Microsoft's recent purchase of Facebook partner Skype.