1) Depreciator 2) Detractor 3) Disparager 4) Knocker 5) Mudslinger 6) Tarbell 1) Mudslinger 
The term muckraker refers to reform-minded journalists who wrote largely for all popular magazines and continued a tradition of investigative journalism reporting; muckrakers often worked to expose social ills and corporate and political corruption. Muckraking magazines—notably McClure`s of publisher S. S. McClure—took on corporate monopolies....
any of a group of American writers, identified with pre-World War I reform and exposé literature. The muckrakers provided detailed, accurate ... [6 related articles]
[n] - one who spreads real or alleged scandal about another (usually for political advantage)
mudslinger noun one who spreads real or alleged scandal about another (usually for political advantage)