Good question. Here's the best summary I found. Note, it's an article from 2012. Search "facebook dual class stock structure" if you want to see much more that

Good question. Here's the best summary I found. Note, it's an article from 2012. Search "facebook dual class stock structure" if you want to see much more that has been written on the topic. "A string of voting arrangements outlined in Facebook’s SEC filing show that some of the company’s most powerful shareholders have ceded their voting rights to Zuckerberg, the company’s chief executive. While Zuckerberg only owns 28.2 percent of the Facebook’s shares, the additional “shares subject to voting proxy” gives him an additional 30.6 percent of the voting power, leaving him with a total of 56.9 percent of the shareholder voting power. That gives Zuckerberg full control of the company’s decisionmaking. Under the arrangement, Dustin Moscovitz, Sean Parker, and a host of other Silicon Valley bigwigs have given Zuckerberg “irrevocable proxy” to control their votes. That means that their shares will swing with his shares. Zuckerberg also has irrevocable control over shares held by DST, Greylock, Accel Partners, and other major firms and investors — and the voting rights that go along with those shares — in most circumstances. “This is not common at all,” said Menlo Ventures partner Mark Siegel, who has monitored quite a few IPOs in his time in Silicon Valley and spoke to VentureBeat by phone today. “He negotiated a very unique deal,” said Siegel of Zuckerberg’s coup. While no one knows exactly why Moscovitz, Parker, and a slew of high-powered VC firms would have given up their votes, Siegel speculated, “I’m sure there’s a point where shares were offered with that as a contingency.”" https://venturebeat.com/2012/02/01/zuck-power-play/ https://venturebeat.com/2012/02/01/zuck-power-play/