Claim: Adolph "Harpo" Marx changed his name to "Arthur" in order to avoid an association with German dictator Adolph Hitler.
Origins: An age-old technique for mobilizing a populace to fight a war is to completely demonize the enemy so that the conflict is seen as a moral battle rather than a political one. This technique was used to maximum effect in America during World War I,
when for the first time the USA was engaged as a late entrant to an overseas war, one which many Americans wanted no part of. Accordingly, the Germans were recast as "Huns" to whom all sorts of atrocity tales were attributed. Suddenly everything Germanic became anathema — German-Americans sought to avoid being branded as disloyalists, traitors, or spies by declaring themselves to be Dutch or anglicizing their names, and common items with German names were retitled: sauerkraut became "victory cabbage," hamburgers turned into "liberty sandwiches," and "hamburger steak" was henceforth known as "Salisbury steak." And a young comic named Julius Marx, who came from a German family and was touring America in a vaudeville show his three brothers, altered his stage character from German to Yiddish, then finally to American. Julius would, of course, later became nationally famous as Groucho, one of the celebrated Marx Brothers.
The renaming frenzy didn't carry over to World War II (in part because the Nazis did such a thorough job of demonizing themselves), but one result of the Nazi era in Germany was the long-lasting stigmatization of the names "Adolph" and "Hitler," as thousands of people (on both sides) bearing these names changed them in order to avoid any association with the notorious German dictator. So when Marx Brothers fans eventually learned that Arthur "Harpo" Marx had been born Adolph Marx, they naturally assumed he had changed his first name for similar reasons. But this was a retroactive explanation for a transition that had actually taken place many years earlier.
Little Adolph Marx had quickly been nicknamed "Ahdie," a name he much preferred to "Adolph" — so much so that he eventually adopted the name "Arthur" in place of his given name. When, exactly, Adolph became Arthur is difficult to pin down, but the change seems to have been effected by 1911, and he was identified as "Arthur" in newspaper reviews of Marx Brothers performances as early as 1913 — long before the world had heard of an Austrian named Adolph Hitler, well before the outbreak of World War I, and even a few years before that momentous day when he was tagged with the moniker of "Harpo."