Former UnitedHealth Group chief executive officer Stephen Hemsley to replace Andrew Witty. Here's what we know.

Stephen Hemsley ran UnitedHealth Group for more than a decade. It's a different company after four years with Andrew Witty in charge.

Witty’s departure was surprising, though it follows a sharp downturn in the healthcare juggernaut’s financial outlook. He is being replaced by Stephen Hemsley, the chair of UnitedHealth’s board and a previous chief executive.

UnitedHealth Group CEO Stephen Hemsley, returning to run the healthcare giant after Andrew Witty resigned, said he has the right strategy in place “for the era ahead.”

"We are grateful for Andrew's stewardship of UnitedHealth Group, especially during some of the most challenging times any company has ever faced," Hemsley said. "The Board and I have greatly valued his leadership and compassion as chief executive and as a director and wish him and his family the best.