Warren Buffett's Berkshire Hathaway, became the biggest shareholder in Bank of America Tuesday, the second largest U.S. bank, exercising warrants to buy 700 million shares at below-market prices, WSJ reports. He made about $13 billion on the deal, which was initiated in 2011 when he bought preferred shares in the bank amidst the financial crisis.

Why it matters: This makes Buffett the largest shareholder of both the second and third largest U.S. banks (the third being Wells Fargo). Per Reuters data, he's got 6.6% in Bank of America and 10% in Wells Fargo.