Before he arrived at Geisinger in 2016, Jaewon Ryu, an emergency medicine doctor with a law degree, held a raft of leadership roles in health care, insurance, and government, including at Kaiser Permanente, Humana, and the Centers for Medicare and Medicaid Services. He joined the Pennsylvania-based health system as an executive vice president and chief medical officer, and this December became interim president and chief executive officer when its former CEO David Feinberg headed to Google to lead its health care strategy.