"While in office, Roosevelt became a "trust buster" by forcing the great railroad combination in the Northwest to break apart. As President, Roosevelt saw himself a representative of all the people, including farmers, laborers, white collar workers, and businessmen. Roosevelt therefore was focused on bringing big business under stronger regulation so that he could effectively serve all the people he represented. He sought to regulate, rather than dissolve, most trusts. Efforts continued over the next several years, to reduce the control of "big business" over the U.S. economy and workers. Earlier Congress passed the Sherman Antitrust Act in 1890 to maintain economic liberty, and to eliminate restraints on trade and competition. This act came into play during Roosevelt's trust busting activities. " - http://www.nps.gov/history/logcabin/html/tr3.html

Basically, if Congress is owned by corporations, TR was the biggest anti-corporatist out there. He was against big business and monopolies, doing things that helped white collar workers are the expense of big business.

His administration was instrumental at reversing the trend of the degrading quality of food, and the abuse of workers' rights. If it wasn't for him and the Congress at the time, we could've had a communist uprising down the line.