Money | Twitter Twitter CEO Evan Williams Steps Down, COO Promoted Dick Costolo will head day-to-day operations By Nick McMaster Posted Oct 4, 2010 4:31 PM CDT Copied Dick Costolo, chief operating officer at Twitter, speaks during his keynote presentation at the Ad Age Digital Conference in New York, Tuesday April 13, 2010. (AP) Twitter co-founder and CEO Evan Williams is relinquishing leadership of the microblogging site to COO Dick Costolo, reports the Wall Street Journal. "Building things is my passion," Williams offers as explanation for the move, adding that he asked Colstolo to take over. Adds Costolo, recently "it became clear to everybody that Ev's got to be able to focus on product strategy." The move also comes as Twitter looks to reap some sort of profitability out of its explosive growth. Read These Next Iran's new leader issued a defiant first statement. Country star cancels rest of his tour: 'I am mentally unwell.' Second 'Doomsday Plane' in 2 months is seen over California. Report finds uninjured cop took an ambulance as a dying man waited. Report an error