If any investor has stood the test of time, it is Warren Buffett, and with good reason. For years, the “Oracle of Omaha” has had a rock-star-like presence in the investing world, and his annual Berkshire Hathaway shareholders meeting draws thousands of loyal fans who are investors.

According to Berkshire's most recent filing, which is as of June 30, it has bought approximately 5 million shares of UnitedHealth Group. It's a notable position for Berkshire, but it's not a huge one -- UnitedHealth accounts for just 0.5% of its total portfolio.