Mario Gabelli has made nearly 6,200% over the decades on Berkshire Hathaway stock, showing the power of buy-and-hold investing. : Value investor Mario Gabelli told CNBC on Monday that he first started buying shares of Warren Buffett's Berkshire Hathaway back in 1986. Decades later, he's made more than 60 times his money, illustrating the power of buy-and-hold investing. In an interview on "Squawk Box," the Gamco Investors CEO said the purchases were for two of his mutual funds: Gabelli Equity Trust and Gabelli Asset Fund. The funds began investment operations a few months apart in 1986.