also muckraker, c. 1600, "one who rakes muck" (earliest use is in a figurative sense: "a miser"), from muck-rake "rake for scraping muck or filth" (mid-14c.), from muck (n.) + rake (n.). The figurative meaning "one who inquires into and publishes scandal and allegations of corruption among political and business leaders" was popularized 1906 in speech by President Theodore Roosevelt, in reference to the "man ... with a Muckrake in his hand" in Bunyan's "Pilgrim's Progress" (1684) who seeks worldly gain by raking filth.
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. [T. Roosevelt, quoted in "Cincinnati Enquirer," April 15, 1906.]
Muck-rake (n.) in sense "person who hunts scandal" is attested from 1872. To muck-rake (v.) in the literal sense is from 1879; figuratively from 1910. Related: Muck-raking.