Warren Buffett is the largest shareholder and chairman of Berkshire Hathaway. Buffett began purchasing shares of Berkshire Hathaway in 1962, and by 1969 focused all of his attention on running the company until it became one of the largest holding companies in the world. Buffett is known to buy 'wide moat' businesses with attractive and sustainable returns on capital and long term business predictability. He claims he invests only in companies that he understands and therefore has no exposure to technology stocks and is heavily invested in insurance companies. Buffett sees himself as a capital allocator within Berkshire Hathaway, whose primary responsibility is to allocate capital to opportunities with the highest returns. That has recently involved purchasing controlling stakes in companies and maintaining their management teams. Warren Buffett's writings are available in The Essays of Warren Buffett and (to a lesser degree) in Warren Buffett Speaks: Wit and Wisdom from the World's Greatest Investor. Numerous books about Warren Buffett have been published.