AMC, the world's largest movie-theater chain, is now over 80% owned by everyday investors. Which means CEO Adam Aron has a new boss: The 'apes.' WSJ's Alexander Gladstone and Erich Schwartzel introduce the online movement that saved AMC. And self-declared 'ape' investor David Dumas explains why he jumped in. Learn more about your ad choices. Visit megaphone.fm/adchoices