Who's This? The patriot on page 22 of Who's Who vol.XV.
How you could have heard of him: He played an important role in the Elseworlds mini-series Golden Age, and was behind starting Hero Hotline in the mini-series of the same name (as The Coordinator), something revealed by writer Bob Rozakis, but not by the comic itself. While Tex has appeared in a JSA Returns special, the Mr. America identity has since been taken over by the next generation, Trey Thompson, in a very similar costume.
Example story: Action Comics #42 (1941) by Bernard Baily
Bernard Baily is perhaps better known as the co-creator of the Spectre and Hourman for a reason...
Who else? If I were completely insane, I might have attempted to do the various members of the Monster Society of Evil. I still might some day. No, I think we're ready to move on to volume XVI of Who's Who. Place your bets!