UnitedHealth Group Inc. on Wednesday named Brian Thompson the CEO of UnitedHealthcare.Thompson, who's been with the Minnetonka insurer since 2004, most recently was CEO of UnitedHealthcare's government programs including the Medicare & Retirement and Community & State businesses. He replaces Dirk McMahon, who was promoted in Feburary to become president and chief operating officer of UnitedHealth Group, part of the C-suite changes brought on by the appointment of Andrew Witty as CEO of UnitedHealth Group.