late 14c., "one who handles" anything, agent noun from handle (v.). Specific sense of "one engaged in trade" is from 1690s; that of "prizefighter's assistant" (1916) was earlier used in reference to dogfights and cockfights (1825).
A person who seconds, supports, advises, etc, a principal: Bush and his political handlers believe, as Reagan did, that the way to the people's heart is paved with unshucked corn
Related Terms[1950+ Prizefighting; the term was used of those who handled gamecocks, dogs, etc, by 1825]