Apparently Hank Williams Sr. nicknamed Hank Williams Jr. “Bocephus” from a ventriloquist dummy used at the Grand Ole Opry.
But there’s more to the story. One old set of lyrics to “The Arkansas Traveler” apparently is about a boy named Bosephus and a fiddling bear! (Albert Bigelow Paine, children’s author and biographer of Mark Twain, was inspired to write a whole bookful of stories about their adventures. It’s called The Arkansaw Bear: A Tale of Fanciful Adventure Told in Song and Story. There’s also a sequel, The Arkansaw Bear and Elsie. Modern copies spell it “Arkansas”.)
Wasn’t it likely that the Grand Ole Opry audience were expected to know that Bocephus came from “The Arkansas Traveler”? (Did the ventriloquist have any bear dummies in his act?)
The interesting thing about the name etymology is that the song initially just identifies the boy as “a boy named Bo“. (Really, “Beau”.) Only later do the lyrics spin it out: “And his folks are still waiting for Bosephus to come back.” This suggests that the kid’s first name is indeed Beau, and that “sephus” (see-fus) is really a corruption of his last name (or something else – “carcass” might be too crude).
If you could find out where the song came from and the local family names, you could probably make a shrewd guess. “Bo Seavers” or something like that would make perfect sense.
Alternately, it could be some French word. “Beauregard” = “Beau” + “regard”. What French word sounds like “Sephus”?
Or it could be that the boy’s name was really “Joe” (a name that shows up in another set of “Arkansaw Traveler” lyrics), in which case “Josephus” would be quite in order.