David Sokol, long considered by outsiders to be the most likely candidate to succeed Warren Buffett, resigned from Berkshire Hathaway Inc. after purchasing shares of a company he suggested Mr. Buffett buy.

Mr. Buffett, Berkshire's chief executive and chairman, said in a statement Wednesday that Mr. Sokol had told him he owned shares in the chemical company, Lubrizol Corp., when they first discussed the deal in January. Mr. Buffett said "neither Dave nor I feel his Lubrizol purchases were in any way unlawful" and weren't a...