Now, a Scottish butcher who has been researching the subject has announced that haggis was not invented in Scotland at all. It was brought there... by the Vikings. Seriously.
Apparently the word "haggis" itself appears to be of Scandinavian origin, arising from the Old Norse word haggw, which means to hack into pieces. The earliest written recipe known in Scotland dates to about 1430 CE. The butcher on whose research this claim is based, Joe Callaghan, also states that haggis, which is usually made from sheep, should actually be made from venison, since deer are indigenous to Scotland and sheep are not. If you'd like to order some "staggis" from Mr. Callaghan's shop, go here.