Today's OED antedating: "character assassin"

Character assassin, defamer of reputations ("character," n., sec 19, first use cited 1951): Book titled Ade’s Fables, by George Ade, 1914, p 183: "About the time he came up for re-election, a lot of Character-Assassins tried to shell-road him and hand him the Gaff and crowd him into the 9-hole."