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Dustin Moskovitz, Mark Zuckerberg's Harvard roommate, recently stopped speaking to him. This has made things awkward at Facebook's Palo Alto campus, as Moskovitz is the last reminder walking around that Zuckerberg was not Facebook's sole founder. The two have resumed talking, but Moskovitz, seeking to dissociate himself from his college chum's creation, had dropped the title of vice president and asked for his bio and photograph to be taken off the company's PR website. He's now taken the title of "technical lead," and is working behind the scenes on Facebook's infrastructure. (Moskovitz was not always so publicity-shy: He gladly spoke about Facebook's wireless initiatives at the CTIA conference last fall, and, in a comment left after this post was published, denies a rift and blames Valleywag for his lowered profile.) Why the reported split, after they've worked together so long?

Zuckerberg and Moskovitz are both known to be stubborn and to argue vociferiously for their ideas. It's hard to imagine a disagreement that would cause a permanent rift.

This split appears to have something to do with the pair's Harvard history. A clue lies in a 2005 Denver University newspaper article about Facebook. In it, Moskovitz's title is given as "No Longer Expendable Programmer." Clearly an inside joke, but where did it come from? We hear that Zuckerberg referred to Moskovitz as "expendable" and "a soldier" in IM conversations turned up during Facebook's long-running lawsuit with the founders of rival social network ConnectU.

That lawsuit was reportedly settled earlier this month. Moskovitz was clearly familiar with the "expendable" remark. The feud is, insiders tell me, only goes back a month. How to explain these facts? Here's a theory: Back in 2005, Zuckerberg must have convinced Moskovitz to laugh off the slight. Could the final stages of the legal process turned up evidence that persuaded Moskovitz Zuckerberg wasn't joking?

If so, Zuckerberg may face a lonely future. Chris Hughes, the only other person Zuckerberg acknowledges as a cofounder, left Facebook to work on Barack Obama's campaign. Andrew McCollum and Eduardo Saverin, two Harvard classmates sometimes identified as cofounders, have long been out of hte picture. Moskovitz is the only person who has been with Zuckerberg since the beginning, the only comrade who remembers Facebook's long march out of collegiate obscurity.

Google's Larry Page and Sergey Brin made a pact to work with each other for 20 years. In two decades, who will Zuckerberg have in his trusted inner circle? Or does he view everyone around him, as he once labeled Moskovitz, as "expendable"?