The Karakachan Dog (also known as Bulgarian Shepherd Dog) is a very old breed. They are said to be the descendant of the ancient domestic dogs of the Balkans and were used by nomadic shepherds centuries ago. It's possible that the original stock for these dogs came from Afghanistan and Iran when the people of the Balkans came from those areas.
The Karakachan breed of dog is an outstanding livestock guarding dog but they are very serious about their work. They will attack to defend their flocks and property. If you intend to keep a Bulgarian Shepherd Dog as a pet then you need to make sure that they are very well socialized from the time they're a puppy. These are very loyal and brave dogs and they are devoted to their families. It's part of their nature to be territorial and protective.