Singer, through his hedge fund, Elliott Management, has developed a unique, and profitable, brand of adversarial investing. On May 18, 2017, Jonathan Bush was standing at the stern of his luxury catamaran, the Zenyatta, named for a champion Thoroughbred racehorse, when he received a text message from a colleague warning him not to answer calls from phone numbers he didn’t recognize. Bush, the co-founder and C.E.O. of the health-care technology company Athenahealth, had just finished a three-day race with his company’s sailing team, going from the Bahamas to Bermuda.