I told MarketWatch readers on Aug. 14 that Warren Buffett was about to reveal one big mystery elephant for Berkshire Hathaway’s portfolio — one $5 billion investment in the shares of an industrial giant.

Shares of UnitedHealth Group are surging before the market open Friday as Warren Buffett’s Berkshire Hathaway disclosed that it recently purchased shares of the beleaguered insurer.

While this confirms our earlier evaluation that the stock seems attractively priced, the underlying operational challenges still exist—medical cost ratios sitting at 89.4%, compressed profit margins,...

At Berkshire Hathaway’s annual meeting earlier this year, Warren Buffett showed just how much of a fan he is of Apple’s CEO, Tim Cook. “Tim Cook has made Berkshire a lot more than I have made Berkshire,” Buffett said to laughter in the room. It was funny, but considering that Apple is Berkshire’s largest holding, I don’t think it was hyperbole.