Warren Buffett once wrote to shareholders of Berkshire Hathaway Inc. that if he, his partner Charles Munger and his deputy Ajit Jain were ever on a sinking boat and only one of them could be saved, “Swim to Ajit.”

On Saturday, Mr. Munger solidified Mr. Jain’s importance to the future of Berkshire when he hinted that the 63-year-old head of the conglomerate’s reinsurance business is part of what appears to be a two-man race to don the chief-executive hat once Mr. Buffett, 84, is no longer around.

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