Muckraking magazines—notably McClure's of publisher S. S. McClure—took on corporate monopolies and crooked political machines while raising public awareness of chronic urban poverty, unsafe working conditions, and social issues like child labor.
The muckrakers are most commonly associated with the Progressive Era period of American history. The journalistic movement emerged in the United States after 1900 and continued to be influential until World War I, when the movement came to an end through a combination of advertising boycotts, dirty tricks and patriotism.
Before World War I, the term "muckraker" was used to refer in a general sense to a writer who investigates and publishes truthful reports to perform an auditing or watchdog function.
In contemporary use, the term describes either a journalist who writes in the adversarial or alternative tradition, or a non-journalist whose purpose in publication is to advocate reform and change. Investigative journalists view the muckrakers as early influences and a continuation of watchdog journalism.
The term is a reference to a character in John Bunyan's classic Pilgrim's Progress, "the Man with the Muck-rake" that rejected salvation to focus on filth. It became popular after PresidentTheodore Roosevelt referred to the character in a 1906 speech; Roosevelt acknowledged that "the men with the muck rakes are often indispensable to the well being of society; but only if they know when to stop raking the muck..."
Source and Lot's More
"Ida Minerva Tarbell (November 5, 1857 – January 6, 1944) was an American teacher, author and journalist. She was one of the leading "muckrakers" of the progressive era. She wrote many notable magazine series and biographies. She is best known for her 1904 book The History of the Standard Oil Company, which was listed as No. 5 in a 1999 list by New York University of the top 100 works of 20th-century American journalism. She depicted John D. Rockefeller as crabbed, miserly, money-grabbing, and viciously effective at monopolizing the oil trade."
Source and Lot's More
"The Brass Check is a muckraking exposé of American journalism by Upton Sinclair published in 1919. It focuses mainly on newspapers and the Associated Press wire service, along with a few magazines. Other critiques of the press had appeared, but Sinclair reached a wider audience with his personal fame and lively, provocative writing style. Among those critiqued was William Randolph Hearst, who made routine use of yellow journalism in his widespread newspaper and magazine business.
Sinclair called The Brass Check "the most important and most dangerous book I have ever written."(p. 429)  The University of Illinois Press released a new edition of the book in 2003, which contains a preface by Robert McChesney and Ben Scott.
The text is also freely available on the Internet, as Sinclair opted not to copyright the text in an effort to maximize its readership.
For much of Sinclair's career he was known as a "two book author": for writing The Jungle and The Brass Check. Sinclair organized ten printings of The Brass Check in its first decade and sold over 150,000 copies. To maximize his readership, he did not take advantage of the opportunity to copyright the book."
Source and More
"Upton Beall Sinclair, Jr. (September 20, 1878 – November 25, 1968), was an American author who wrote close to one hundred books in many genres. He achieved popularity in the first half of the twentieth century, acquiring particular fame for his classic muckraking novel, The Jungle (1906).
It exposed conditions in the U.S. meat packing industry, causing a public uproar that contributed in part to the passage a few months later of the 1906 Pure Food and Drug Act and the Meat Inspection Act. In 1919, he published The Brass Check, amuckraking exposé of American journalism that publicized the issue of yellow journalism and the limitations of the “free press” in the United States. Four years after the initial publication of The Brass Check, the first code of ethics for journalists was created. Time magazine called him "a man with every gift except humor and silence." In 1943, he won the Pulitzer Prize for Fiction.
Sinclair also ran unsuccessfully for Congress as a Socialist, and was the Democratic Party nominee for Governor of California in 1934, though his highly progressive campaign was defeated rather soundly."
Source and More