Lincoln Steffens, Ida Tarbell, and Upton Sinclair were muckrakers. What did they do?

Muckrakers were a group of writers, including the likes of Upton Sinclair, Lincoln Steffens, and Ida Tarbell, during the Progressive era who tried to expose the problems that existed in American society as a result of the rise of big business, urbanization, and immigration. Most of the muckrakers were journalists.