Final answer:
Hugh Hefner is not a muckraking journalist; he is known for founding Playboy magazine. Muckrakers like Ida Tarbell exposed corporate and political corruption during the Progressive Era.
Step-by-step explanation:
The individual who is not a muckraking journalist among the options provided is Hugh Hefner. Muckrakers were investigative journalists who exposed social ills and corporate and political corruption during the Progressive Era. Examples of famous muckrakers include Ida Tarbell, who investigated the monopolistic practices of the Standard Oil Company, Jacob Riis, a pioneer in photojournalism who highlighted poor living conditions in New York City's tenements, and Upton Sinclair, whose novel "The Jungle" led to food safety reforms. In contrast, Hugh Hefner was the founder of Playboy magazine and is not associated with the muckraking movement.