Ken Griffin, Founder, CEO and Co-chief Investment Officer at Citadel, speaks during the Milken Institute Global Conference REUTERS/Mike Blake (New York, NY) — Mayor Mamdani’s very public battle with a billionaire over the last few weeks could end up losing the city billions of dollars. The socialist mayor, who ran on a campaign of “taxing the rich” to help fix the big apple’s biggest financial problems, finds himself in very public back and forth with Citadel hedge fund CEO, Ken Griffin.