Warren Buffett's biographer says he's 'literally not replaceable' as Berkshire Hathaway enters a new era

Warren Buffett announced his plan to step down as CEO of Berkshire Hathaway. Getty Images / Michael Buckner Berkshire Hathaway CEO Warren Buffett announced Saturday he plans to resign at the end of the year. The iconic investor built Berkshire into a trillion-dollar empire over the last 55 years…