The Great Pyrenees began as a livestock guardian in the mountains between France and Spain, where big white dogs stayed with flocks and watched for wolves and bears. That history explains a lot: a giant, thickly coated dog with a plumed tail, double rear dewclaws, and a habit of deciding things for itself.
Many Pyrs are gentle and devoted at home, but they can be independent, slow to obey and inclined to bark at night or roam. Expect heavy shedding, a protective streak and a need for secure fencing. In Gilbert's hot desert, the thick coat also means managing heat carefully. Pyrs and Pyr mixes show up often in shelters and rescues, and each dog's personality varies.