Founded in 1847, the paper first came to attention before and during the American Civil War under the leadership of Joseph Medill, an abolitionist and supporter of Abraham Lincoln. The paper remained a strong force in Republican politics for years afterwards.
Under the 20th century editorship of Col. Robert R. McCormick these tendencies were exaggerated and the paper was strongly isolationist and actively biased in its coverage of political news and social trends, calling itself "An American newspaper for Americans", excoriating the Democrats and the New Deal, resolutely disdainful of the British and French, and greatly enthusiastic for Chiang Kai-shek and Sen. Joseph McCarthy. These biases were so pronounced that the paper came to be regarded as untrustworthy.
One of the great scoops in Tribune history was the revelation of U.S. war plans on the eve of the Pearl Harbor attack. Col. McCormick also once mutilated an American flag by cutting out what he deemed the "Rhode Island star" after that state had offended him.
Although the paper has since reformed and toned down, it retains a strong Republican slant and remains a dominant voice in "Chicagoland" and the Midwest in general.
The Chicago Tribune is the centerpiece of The Tribune Corporation, which includes many smaller suburban newspapers, radio and television stations, including WGN, whose call letters stand for "World's Greatest Newspaper", as well as pulp and paper interests, and Great Lakes shipping. The Tribune Corporation also owns the Los Angeles Times and the Chicago Cubs baseball team.
The corporation is also closely associated with the New York Daily News. The publisher of the News, Capt. Joseph Patterson and Col. McCormick, were both descendants of Medill. Both were also enthusiasts for simplified spelling, another hallmark of their papers.