Berkshire Hathaway, led by Warren Buffett, has recently invested in UnitedHealth Group despite its 40% stock decline this year. The investment aligns with Buffett's strategy, focusing on UnitedHealth's strong brand, cash flow generation, dividend growth, and stock buybacks. With a P/E ratio of 13x, near five-year lows, UnitedHealth appears undervalued, presenting a potential opportunity for value investors.