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

UnitedHealth has faced several headwinds in the recent past, ranging from a cyberattack, which had greater than initially realized impacts, to the tragic killing of its CEO, which caused the company to suffer harsh public backlash over the company's and industry practices.

His time at the helm was also marked by a major cyberattack that compromised the data of 190 million people, as well as scrutiny over the company’s Medicare billing practices.

Stephen J. Hemsley returned as CEO after Andrew Witty's surprising decision to leave the insurance giant. UnitedHealth's stock fell 17% on Tuesday.

Even UnitedHealth will struggle to overcome parasitic medical costs that Warren Buffett once called a tapeworm eating away at U.S. economic competitiveness. The $300 billion healthcare conglomerate reinstalled Chairman Stephen Hemsley as CEO and yanked its financial guidance.

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

Robyn Denholm has earned five times as much as UnitedHealth Group's Stephen Hemsley, the next non-executive chair most prone to liquidating stock.

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.