Let’s get the two guys out of the way first. Here’s what I found: the names are common in old French carols, where they are rendered as “Guillô” and, well, “Robin.” The French version of “Willie” is pronounced “Gwee-yo.” Robin’s name is “Ro-bɛ̃,” with that funny-looking “e” being fairly nasal and the “n” not really being pronounced at all—it’s just a marker for the nasal sound. Everybody got that? Anyway, I’m sure if I dug around long enough I could discover why these two names are sort of generic, but I’ll leave it at that, because there’s more ground to cover here. You can just figure that Willie and Robin are like Jack and Jill, or Jim and John, or Lucy and Ethel.
Whatever. On to the author and origin of the song. Didn’t you just assume, if you thought about it at all, that this was a folk song? It’s not, since it has a known author, the poet Bernard de la Monnoye, who lived from 1641-1728. What a