Bill Ackman is the Founder, Chief Executive Officer, and Portfolio Manager of Pershing Square Capital Management. He has made a name for himself as one of the most vociferous activists in investing. While he often draws comparisons to Carl Icahn, Ackman believes he mirrors Warren Buffett more closely. In a 2013 interview, he outlined his strategy for investing as relying on concentrated research to identify great businesses that es that are trading at highly discounted valuations. Ackman also uses using his stake in a company to intervene in the decision-making, strategy, management, or structure of the businesses that .