What does the "Q" stand for in John Q. Public?

You know John Q. Public. He’s the dude who lives at 123 Main St. in Anytown, USA. He’s married to Jane Q. Public. You know the chap. Anyway, I’ve searched online and I still can’t find out what his middle name really is, but I’m guessing some of you know.

And then there’s Jesus H. Christ…