I have heard that Florida hogs are descended from what the Spanish brought over in the 1500s. I have seen two feral hogs, together, while hiking alone and unarmed in the Cape Canaveral seashore in Florida. I was about ten feet away from one when I took a picture of it, and the sound of the camera scared them into the bushes.
Yep, De Soto I believe. At various other times other populations have been introduced to other parts of the US, usually by accident.