Dustin Moskovitz thought he might go to business school. Or graduate school. Maybe he would work in technology. Mostly he just wanted to graduate.

It was early 2004 and Moskovitz was in his second year at Harvard, majoring in economics and living with roommates Chris Hughes, Billy Olson and Mark Zuckerberg. Zuckerberg, also a sophomore, had already started to make a name for himself on campus, first with the release of Course Match, a tool to help students find out which courses their classmates were taking, and then with Facemash, a website similar to Hot or Not.

Moskovitz didn't know Zuckerberg before moving in with him — they were randomly paired together — but the two quickly became friends. Still, he wasn't exactly floored by these early projects, or at least not by Facemash. "It just seemed a little trivial at first," he says.

Zuckerberg's new project was different, though. Harvard had repeatedly said it would combine its various campus directories — what it called "facebooks" — into one easily searchable online database. One big Facebook. Harvard continued to delay building it, which Moskovitz felt was "ridiculous," so Zuckerberg decided he would. On Feb. 4, 2004, Zuckerberg launched TheFacebook.com.

"When he was just launching the thing, he just needed some administration help, which was part of my skill set at the time," Moskovitz says. "I didn't really pitch him. It was more like he was working on this thing and I was sitting next to him, and he would say, 'Hey, can you help me with this?'"

The very first thing he worked on with Facebook was configuring the email server.

See also: The Agony and the Ecstasy of Growing Old With Facebook

The social network quickly spread throughout Harvard. Moskovitz recalls walking around the campus in those early days "and seeing Facebook up on peoples' computers." Three weeks after launching there, it expanded to Columbia University, and then to Stanford and Yale by the end of February.

"Once we got going with the Facebook idea and it got popular at Harvard, we had a pretty good inkling that social networks were going to be pretty big," he says. "We were not totally confident that ours would be the one to be pretty big, but we were confident that one would."

That summer, Moskovitz moved with Zuckerberg to a rented house in Palo Alto and committed himself to a startup that would take him on a whirlwind journey for four years, have him overseeing nearly 200 employees and eventually turn him into America's youngest billionaire.

"It was kind of like an evolution of seriousness of the company," he says. "When we first left school for the summer, we thought we were coming back in the fall. And then it eventually became dropping out. But at each of those phases, it felt like it was the appropriate thing to do."

Ezra Callahan (in the costume), Facebook employee #6, in a meeting with Mark Zuckerberg (left) in 2009. Image: Ezra Callahan, Facebook

Ezra Callahan was nearly broke when he opened the email from Sean Parker: "What are you doing?"

What was he doing? He was sitting in front of a shared computer at a youth hostel in Dublin, trying to come to terms with the fact that the money he'd saved up during college had all but run out. His European jaunt couldn't go on much longer. Soon, he would have no choice but to move back to his parents' home in Los Angeles for the next six months until it was time to start law school.

"Come work at Facebook," Parker wrote in the email.

This wasn't the first time Parker had emailed Callahan out of the blue. After graduating from Stanford in 2003, Callahan moved into a rented house with five college friends. There was still one bedroom vacant so the group messaged a few different Stanford email lists to find someone to take it. Parker was the first person to respond.

"At the time, we were like, 'Isn't that the Napster dude?'" Callahan remembers. "I don't exactly know how our email found its way to him."

Parker launched Napster in 1999 when he was just 19, upending the music industry and setting off a wave of lawsuits from record labels and big name recording artists. Two years later, he and two Stanford students launched Plaxo, an online address book tool. He was nearly broke at the time and stayed with a series of friends until the startup raised some funding. In July 2003 the 23-year-old Parker moved into a house with five random Stanford students.

For the first six months or so, the roommates rarely saw him; Parker was entirely consumed with Plaxo. Then, in early 2004, he was kicked out by the startup's investors. After that, Callahan says, "he was around all the time and we became friends."

By the time Callahan received Parker's email at the hostel in December 2004, the roommates had disbanded and Parker had found his next big thing, Facebook, and with it a new house to crash at. Parker first met with Zuckerberg in New York not long after it launched, but it wasn't until the summer of 2004 when he bumped into Zuckerberg on the street near the house Facebook's small team had rented in Palo Alto, Calif., that he was invited to join the company. Parker became Facebook's first president, and for a brief time, a roommate at the Facebook house.

Callahan didn't know any of this at the time. He had heard of Facebook early on and saw it spread quickly across the Stanford campus, but he didn't feel its impact directly. Most of his friends had graduated already and had not joined the college-focused social network. But after going back and forth with Parker by email, he decided working at the startup would at least be better than moving in with his parents.

Three weeks later, he showed up on the doorstep of the Facebook house and announced that he had been hired by Parker and was moving in. It was after midnight and no one else on the team had been told.

Just like that, he became Facebook employee No. 6, tasked with developing a local business product to prove to investors the social network could generate revenue. His only qualification, and the reason Parker reached out to him in the first place, was that he had spent some time selling ads for the Stanford Daily, the campus newspaper.

"I went to Facebook thinking it was a six-month temporary gig before going to law school," he says. "I never made it to law school."

Soleio Cuervo (left), an early Facebook designer, and Naomi Gleit (right), a product manager in charge of growth efforts. Image: Facebook

Several of Facebook's earliest employees came to the company by chance, thinking they might stay for months only to end up consumed by it for years.

Soleio Cuervo was working as an independent designer in San Francisco in October 2005 when he was contacted by Bryan Veloso, a Facebook designer. Earlier that year, Cuervo had won an award for a website he designed for a friend's little league soccer team. Veloso had also won an award from the same group and stumbled on Cuervo's work that way. Now, he wanted to bring Cuervo in for an interview.

Cuervo made the trip to visit Facebook, which had moved out of the house and into its first office in Palo Alto. The office was relatively empty as Facebook's staff was still small, but those employees who were there were busy "jamming away" on their keyboards. "These guys had this crazy vision," he says, recalling that first meeting. "They were talking about this idea of a [social] graph and accelerating information flow and, if we were perfect, we could graph all the relationships in the world ... A lot of the concepts were pretty well baked; they were just trying to articulate the language for it."

He left the meeting thinking the company's "sheer ambition" was "intoxicating." There was just one problem: Cuervo had never actually joined Facebook. He had graduated from Duke University in 2003, the year before Facebook came out, and never bothered to create an account. So as he walked out of the office building that day, he quickly called up his younger brother who was on the social network and asked for his opinion about it.

"I'll remember his response to my dying day: 'TheFacebook is bigger than God, man. Everybody is on that shit.'"

That response combined with the company's vision was enough to convince Cuervo to come on board. He told himself it might only be for a year; he ended up staying for six. But there was one brief moment when it looked like his time there might be cut short.

About six months after joining, he was working at night alongside Zuckerberg, Moskovitz and a couple designers. Moskovitz randomly turned to him and asked if Cuervo had some "sketchy privacy settings" on his Facebook account because he was having trouble finding Cuervo's profile page. After months of working at Facebook, Cuervo still hadn't created an account because none of his friends were on it yet. Instead, he just logged into his brother's account whenever he needed to. He finally had to come clean and tell Moskovitz.

"I said, 'I don't have an account.' He said, 'What do you mean you're not on Facebook?' He goes, 'You better get an account by tomorrow or I'm firing you,'" Cuervo says. "He was pissed, man."

The next day, Cuervo still hadn't signed up for an account. Rather than fire him, Moskovitz ordered a Facebook engineer to set up an account for him. He went on to design the iconic Facebook Like button.

The Facebook team celebrates raising a round of funding in April, 2006. Image: Kevin Colleran, Facebook

Facebook was started by college students for college students, so it should come as little surprise that the team behaved like college students in the early days.

"Facebook was like college for many of us," says Kevin Colleran, who was hired in early 2005 by Parker to serve as Facebook's first ad sales employee. "We were all young, just out of school, and for most of the team it was their first time having a job."

For Colleran, like his teammates on the West Coast, working at Facebook initially meant living at Facebook. Colleran's apartment in New York doubled as the company's first New York office. As the staff expanded, he says, "many of us teamed up and lived together in the same houses and apartments. We had happy hour every Friday, which led to late nights of beer pong and hanging out."

When Facebook was still headquartered at the house, employees would spend the nights coding, drinking and playing video games. "They were basically nocturnal," Callahan says. He was just about to turn 24 and that made him one of the oldest employees at the company. He felt it, too. "I didn't really like living where I worked. There was an age gap."

Callahan moved out of the Facebook house after two months, but stayed with the company for another five years. Even as Facebook's staff grew over the next couple years and the corporate culture evolved, that age gap persisted.

"The company was so social and there were parties going on," he says, "The people who were older and more established with families, I'm sure for them Facebook's culture was always tricky."

All of that socializing and the immersive work culture clearly had its benefits, though, even for Callahan. He met his wife at Facebook and the couple went on to have a son together. "I bet there are probably 15-20 couples that met at Facebook that got married," he says. "I think we had the second or third Facebook baby."

Mark Zuckerberg at Facebook's headquarters in Palo Alto in 2007. Image: Paul Sakuma/Associated Press

If you ask early employees to pick a defining moment when it became clear that Facebook had grown up and would be around for the long term, most point to Yahoo.

In the second half of 2006, a little more than two years after Facebook first launched, Zuckerberg decided to turn down a $1 billion acquisition offer from Yahoo. At the time, Zuckerberg was just 22 years old, and Facebook was reportedly generating about $30 million in annual revenue and not yet profitable."

"That was a big decision. It was exhilarating," Cuervo says. "We were determined to go big."

This wasn't the first time a business had tried to acquire Facebook. Friendster, an older social network, had made an offer in the early days, as had Viacom, with minimal interest from Zuckerberg.

Callahan remembers Zuckerberg coming out to address a company meeting with the Viacom offer in his hands. "'This is an offer to buy the company,'" Zuckerberg said, according to Callahan, before sticking the offer to a wall. "'Forget that,'" Zuckerberg went on. "'We are not selling the company. We are going to make this happen.'"

But Yahoo's acquisition offer was something else entirely.

"All of us employees could do the math and see how much money of that $1 billion was coming to me," Callahan says. "We were all still really young then. The idea that a lot of us had a couple million dollars at stake, that was a pretty big time to realize we were saying 'no' to that and saying 'full steam ahead' with something bigger."

Zuckerberg's decision to decline the offer is often framed as a lesson to startup founders not to sell too early. In reality, there may have been some luck involved.

"I think most people were in favor of accepting the Yahoo offer, and I think Facebook was prepared to," Callahan says. "And then Yahoo more or less rescinded or lowered the initial offer, which made it easier to say 'no' after that." Marc Andreessen, an early Facebook investor and a member of the company's board of directors, later said Yahoo cut the acquisition offer by $200 million.

"Facebook really came close to accepting the offer," Callahan says. "Most people advising Mark were saying to accept it."

Facebook goes public on May 18, 2012. Image: Richard Drew/Associated Press

Ezra Callahan was rich and about to get even richer. He sat at home on May 18, 2012 watching on television as the little startup he'd joined in 2004 officially became a $100 billion public company. "It was a sentimental day," he says. "It was significant historically and culturally to see the whole world spend a day focused on Facebook."

But it was also a "frustrating day," he says, which turned into a disappointing few months as Facebook stock dropped to as low as half its IPO price. "When the stock price started plummeting, it was really frustrating hearing the media talk about the company like it was some sort of failure," Callahan says. He cared less though about the stock price's impact on his personal wealth. "For us early employees, you are talking about one absurd number versus another."

By the time Facebook went public, there were more than 3,000 people on staff, but most of its early employees had moved on to other projects, each for their own reasons. Cuervo left in November 2011 after realizing there were other things he wanted to accomplish outside the company, and joined Dropbox a year later. Colleran, Facebook's first ad sales employee, left in mid-2011 after trying to "remain involved as long as possible," and joined General Catalyst in early 2012 as a venture partner.

Callahan left Facebook in mid-2010. For years, he never even considered the idea of working elsewhere. Then one day the thought entered his mind and he couldn't shake it. "It was almost like stopping to take a breath after running a marathon and realizing that it's kind of nice to stop running for a second," he says. Callahan didn't do much of anything for a year and then started working in the hospitality industry, opening up a hotel in Palm Springs and a music venue in Los Angeles.

"It's humbling to know I was part of something that became such a phenomenon around the world," he says. "Every day, I recognize how it was just the dumbest luck in the world to have been in the right place at the right time."

The two most notable early employees still at the company are Zuckerberg and Naomi Gleit, who started at Facebook in July 2005 and now works as a product manager on a small team tasked with continuing to grow Facebook's user base.

Unlike some of the other early employees, Gleit actively tried to get a job at Facebook. She had written a paper on Facebook while in college at Stanford and visited Facebook's first office "pretty much every week for a few months" to see if the company was looking to hire anyone. When she finally got hired for a marketing role, she was thrilled, but her mother was disappointed that she didn't become an investment banker instead.

"Sometimes," she says, Zuckerberg and her "reminisce" about the early days of Facebook. But she rarely thinks about what comes next. "So much needs to get done today I haven't really given it too much thought to what comes after Facebook. As long as as I'm learning, I'm happy."

Dustin Moskovitz, cofounder of Facebook and Asana. Image: Asana

Four and a half years after cofounding Facebook and a little more than five years after meeting Mark Zuckerberg, Dustin Moskovitz decided to leave Facebook.

While still at the company, Moskovitz developed software to help streamline Facebook's workflow. It was intended for the engineering team, but was quickly adopted by other departments. As he walked past random desks at Facebook's office and saw the software up and running on peoples' computers, he says he was reminded of how Facebook took off at Harvard's campus years earlier. That was enough to inspire him to launch Asana, a software startup that helps companies manage tasks without email.

When asked what lesson he's taken away from his experience with Facebook, Moskovitz responds, "aiming high."

"Facebook was a very big mission; it really knocked it out of the universe," he says. "It's pretty hard to focus on a small idea after that. You really have to be working on something that you believe will be of similar impact."

A couple months ago, he visited Facebook's headquarters and was struck by how "large" it is now. "It's just Facebook employees everywhere and lots of staff supporting them," he says. "It's pretty different. I've never worked on a campus in any form."

Though he may not be at Facebook anymore, he keeps in touch with many of his former friends and coworkers.

"The people who work at Facebook are people I lived with for many years and people I went to school with, so I definitely still have those relationships," he says. "I see people from that world pretty much every week, including Mark."

Just a few months away from turning 30, Moskovitz has already accomplished far more than most do in their lifetimes, with one exception: He still hasn't graduated from college. He doesn't have much desire or need to at this point, but Moskovitz says he still has the option, based on Harvard's policy for taking a leave of absence.

"With Harvard, you can always go back," Moskovitz says. "I can still go back."