Dick Costolo was the CEO of Twitter from 2010 to 2015; he also served as the COO before becoming CEO. He took over as CEO from Evan Williams in October 2010. On June 11, 2015, it was announced that Costolo would step down as CEO on July 1, 2015 and would be replaced by Twitter co-founder and chairman Jack Dorsey on an interim basis until the Board of Directors could find a replacement.