http://www.quora.com/What-was-Adam-DAngelos-career-timeline-...
Answered by Adam:
"I was in college as an undergrad at California Institute of Technology full time until I graduated in 2006. Facebook launched in spring 2004. In summer 2004 I lived with the Facebook founders in Palo Alto and helped out a little, though I was mainly working on Wirehog, which was a social filesharing network. In summer 2005 I was officially a full time employee at Facebook, and then I took off the next semester from college to keep working at Facebook through the end of 2005. Then I went back to college for the second half of the 2005-2006 academic year, graduated, and went back to Facebook full time after that."
I think Zuck met Adam during high school at Exeter, so they arguably knew one another for a much longer time than the other co-founders.
Maybe that's why you thought that.
I think it's helpful for our international HN cohorts to know that Phillips Exeter[1] is , pretty much, the most elite high school in the US.
I had always thought Adam D'Angelo was a co-founder of Facebook, so I was surprised to not see his name listed in the ownership section.
But Wikipedia lists Dustin Moskovitz, Eduardo Saverin, and Chris Hughes as co-founders in addition to Mark.