Bill Ackman (born May 11, 1966) is an American hedge fund manager. He is the founder and CEO of hedge fund Pershing Square Capital Management LP. Known as an activist investor, Ackman's investment activities routinely make headlines in the financial world. This includes his highly publicised proxy battle and subsequent victory with Canadian Pacific Railway and his recent criticising report on American multi-level marketing firm, Herbalife, calling it a pyramid scheme.