Shares of UnitedHealth Group surged nearly 14% on Friday after billionaire Warren Buffett's Berkshire Hathaway bought 5 million shares of the company, providing a shot in the arm for investors who think the health conglomerate will turn around under its new CEO.

TheStreet. Warren Buffett is arguably the most successful investor of all time. He's amassed an amazingly massive net worth by buying and usually holding stocks for the long haul. Trained under legendary value fund investor Benjamin Graham,

Warren Buffett’s Berkshire Hathaway Inc. took new positions in UnitedHealthcare Group Inc. and homebuilder D. R. Horton Inc., and went deeper into other homebuilding and home-related companies, according to a filing late Thursday.