Speculation about whether Kling was Jewish has persisted over the years. One source says he used the name "Kline" early in his career, a surname that is sometimes (but not always) Jewish. And although he was married to a Jewish woman in a ceremony conducted by a Reform Jewish rabbi, there are questions that have never been fully resolved. The major Jewish newspapers never questioned Kling's Jewishness: writers and reporters frequently referred to him as Jewish, in articles from the 1920s through the 1970s. The Boston "Jewish Advocate" was among those that asserted his real name was John Kline, and said he had even played baseball under that name; one writer said he was "the first of the Jewish pioneers" (Harold U. Ribalow, "Johnny Kling Showed the Way", "Jewish Advocate", 12 April 1951, p. 22). But even earlier, the story of Kling's Jewishness was given a vote of confidence by New York Giants owner-manager John McGraw, who knew Kling and referred to him as a Jewish ballplayer in a 1923 article, "Jewish Baseball Players Wanted" ("American Israelite", 9 August 1923, p. 6). Among contemporary authors who believe he was Jewish is Dr. Gil Bogen, who wrote a book about Kling's life. But some researchers dispute this, and years after his death, his widow Lillian, who was definitely Jewish, seemed to deny that her husband was ever Jewish. In a 1976 "Esquire" magazine article, sportswriter Harry Stein published an "All Time All-Star Argument Starter", consisting of five ethnic baseball teams. Kling was the catcher on Stein's Jewish team. (A reader, however, wrote in and pointed out that Kling was not Jewish but his wife was; and suggested Harry Danning instead.)