Stephen Hemsley has been CEO since 2006.

UnitedHealth Group Inc. (UNH) shares were up 1.23% to $196.89 in premarket trading Wednesday after the company announced that CEO Stephen Hemsley, 65, will be stepping down. 

Hemsley will be succeeded by company President David Wichmann who is 54. Wichmann has also served as the chief financial officer for the company, which is the country's largest health insurer. 

UnitedHealth shares have quadrupled since Hemsley ascended to the post in 2006.

UnitedHealth also announced that Board Chairman Richard Burke would be appointed as the company's lead independent director. Both men will take on their new roles beginning September 1. 

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