UnitedHealth Group CEO Stephen Hemsley, who replaced Andrew Witty, said he has the right strategy in place “for the era ahead.”

Former CEO and current chairman Stephen Hemsley is stepping back into the top job following the abrupt resignation of Andrew Witty, UnitedHealth said.

As CEO for more than a decade, Stephen Hemsley built up UnitedHealth Group, now a $400 billion healthcare behemoth. With his return to the top job, the company will learn whether his playbook still works.

The head of UnitedHealth Group is stepping down, ending a rocky four years marked by rising medical costs, a major cyberattack, and the high-profile killing of an insurance executive.Andrew Witty has left his position as CEO of

The health insurer joins Walt Disney, Starbucks and others in turning to a former leader to guide the company through tough times.

Shares of UnitedHealth Group, Inc. (UNH) fell over 17% on Tuesday after the health insurance giant said CEO Andrew Witty would step down for personal reasons, with chairman and former chief executive Stephen Hemsley taking his place.