Pretty much any sports personality. They constantly put them on commercials, sometimes without names like I am supposed to know who they are. I can tell immediately that they are not paid actors, but without a callout, I don't know (or care) enough to find out.
Paul Tibbets died a few years ago. I had thought he was fairly well known. I was shocked when the news stories of the time portrayed him as an unknown man whose humility prevented him from being a household name.
To be clear I never thought he was as famous as Chuck Yeager, but I did not realize I was one of a tiny minority who knew the name.
He was the pilot of the Enola Gay.
Yeah, same reaction when I'd commented on his passing - kinda surprising how few got the reference.
Almost more surprising was when 'Dick' Winters died. I mean, SURELY people would get THAT reference - aside from any literally or historical point, HBO had that massive series with his character as a major role, but...still, nothing.
To the OP's point, though - I mean, I've been a bit surprised by a few. 'Jackie' Fisher. Alfred T Mahan. etc. Some people who had a rather amazing impact on the current state of the world! However, the MOST shocking? Teddy Roosevelt. I mean, a flippin' US PRESIDENT, and probably the best one we've had - and that's completely ignoring the utterly ludicrous list of his other accomplishments in life.
To say my reaction was 'aghast' would be an understatement... (And it was one of those tree-hugging hippie types, too, which...I mean, this is THE MAN most singly responsible for the National Park system, and you've never heard of him?? The mind boggles...)