Ari at Edge of the West asks,

… who’s the most important … [American] historical figure about whom most people know nothing?

(I have edited the question slightly, because Ari is a historian and so writes 250-word blog posts that have five footnotes.) I don’t have many suggestions, because I am one of the “most people” in this case and ipso facto know nothing about potential contenders. But in the comments someone suggests Philo T. Farnsworth. This reminds me of a conversation I once had with an American historian and a Russian computer scientist. It went something like this:

American: … but that’s TV, I suppose. Philo Farnsworth didn’t know what he was getting us all into. Irishman: Who? Russian: Who? American: Philo Farnsworth. He invented the television. Irishman: No he didn’t. John Logie Baird invented the television! Russian: Who are these people? Television was invented by Alexander Televishnevsky!

I forget the Russian inventor’s real name. As I recall, further discussion established that for many 20th century developments the Russians had a counterpart developer who, according to the schoolbooks, had just gotten there before. And while this may seem like a standard bit of Soviet-era oddness, the phenomenon of simultaneous discovery in science well-established, together with Stigler’s law of eponymy.