Everyone who knows Jonathan Bush—Athenahealth’s CEO and co-founder, who resigned Wednesday following reports of inappropriate behavior—knows he says (and does) things public company CEOs aren’t supposed to say (or do). Still, they probably wouldn’t have cost Bush his job had it not been for Elliott Management, the activist hedge fund that a month ago made a hostile takeover bid for Athenahealth—and which has an unprecedented knack for toppling leaders, corporate and political. I got to know Bush back in 2014 when he was facing another hedge fund manager who was publicly shorting Athenahealth’s stock.