BONUS: Adam D'Angelo was high school friends with Mark Zuckerberg and eventually left Facebook to found Quora.

Employed by Facebook from: November 2006 - June 2008. Although he technically wasn't one of the first 20 employees, D'Angleo was one of Zuckerberg's best high school friends and worked on the social network long before he was on the payroll.

Position at Facebook: CTO

Where he is now: Co-founder and CEO of Quora