I’m reading Everybody Behaves Badly: The True Story Behind Hemingway’s Masterpiece The Sun Also Rises, by Lesley M.M. Blume (which I recommend).
The author recounts that in early 1920’s Paris, Hemingway became the deputy editor for a literary journal called transatlantic review, started by Ford Madox Ford. It didn’t go well. In addition to editorial differences, Hemingway “had begun to suspect that Ford was praising his own work under pseudonyms in the transatlantic (he was correct).”
Apparently sockpuppets have been around since well before the Internet. Plus ça change and all that.