Mark Penn, chairman and CEO of MDC Partners

Mark Penn, the president and managing partner of Stagwell Group, raised industry eyebrows six months ago when he plonked $100 million into the flailing agency holding company MDC Partners—and became its CEO in the process. Six months in, we take a look at what the polarizing pollster has been up to (both in the agency world and the political sphere), what he's learned and where he's taking the holding company.