Here's a bit of comic book history. In 1938, Superman made a big enough debut in comics that it was possible to promote the character at the 1940 New York World's Fair. This is silent home movie footage shot (probably 16mm) at that event on July 3, 1940. There are brief glimpses (very brief) of some of the folks responsible for the Man of Steel's popularity, starting with Jerry Siegel, who's the dark-haired gent with glasses you see at 2:26. Also in there is Harry Donenfeld, publisher and owner of what we now know as DC Comics. He's the one riding the elephant about one minute in…and at 2:14, we see Max C. Gaines and Jack Liebowitz. Gaines is the one who looks like Bert Lahr. He was the guy who recommended to Donenfeld that he purchase and publish the Superman strip that Siegel and artist Joe Shuster had created. Liebowitz was Donenfeld's accountant and he wound up running the company…as accountants usually do.
You will see a gent in a Superman suit riding precariously on a float and popular history would suggest that's Ray Middleton. He was a Broadway actor of the time who, it's been said, was hired to wear the Superman costume at this event, thereby making him the first human being to portray the character. But folks who've studied photos and the film are telling me that ain't Ray Middleton. There seems to be documentation that Middleton did participate in Superman Day at the World's Fair but as a judge in a physical fitness competition. There seems to be no proof he actually donned the famous costume. Since the identity of the guy on the float is unknown, so apparently is the name of the first person to "play" Superman. Maybe he was a reporter or something…
UPDATE: I have corrected the date of the event thanks to Ken Quattro. So thanks to Ken Quattro. Also, I am agnostic on the subject of whether or not that's Ray Middleton in the suit. I'm merely reporting that some people don't think it is.