This could apply to any number of roles, but the one I had in mind was "secretary."
In say, the Middle Ages, a secretary was always a man, and handled the correspondence, (and much of the other businees) of say, a king, noble, or rich man, thereby functioning much like an "executive assistant." This derivation extends to the U.S. President and his Cabinet ("Secretary's of State, Defense, Treasury, etc.)
Around the turn of the nineteenth and twentieth centuries, the introduction of the "typewriter" (and the use of dictaphones and "shorthand" for stenography) automated much of a "secretary's" job, making them available to most executives. Formerly a male province, the role came to be dominated by women, and coincidentally or otherwise, became relatively low paid, with relatively low prestige.
Yet a wise executive will do well to stay on good terms with the "secretary" of his boss or colleague, who is, after all, still the keeper of her (or his) boss's secrets. In his autobiography, T. Boone Pickens relates how he knew that one of his takeover plays was about to succeed when a "secretary" at his target company whispered to him, "You know, Mr. Pickens, not everyone in the board room is against you." (She owned stock in the company and wanted Pickens to take it over.)
Did the 20th century perception of "secretary" as "women's work" lead people to underestimate how "plugged in" secretaries really are in their organizations?