And don't forget it's also used in the classic Elvis song "Trouble" from the movie King Creole.

If you're looking for trouble
You came to the right place
If you're looking for trouble
Just look right in my face
I was born standing up
And talking back
My daddy was a green-eyed mountain jack
Because I'm evil, my middle name is misery
Well I'm evil, so don't you mess around with me

So it's implied here that a Mountain Jack was tough son-of-a-gun.