The English Mastiff, often called simply Mastiff, is a large breed of dog of the general mastiff or Molosser type.This breed is powerfully built, with a massive body, broad skull and head of generally square appearance. It is one of the largest dog breeds in terms of mass, though the Irish Wolfhound and Great Dane are taller.(Wikipedia)
The Mastiff breed is a combination of dignity and courage; calm and affectionate to its master, but capable of protection. This particular mastiff-type breed is an extremely capable guard. If an unfamiliar person approaches near their perceived territory or its master, the Mastiff will immediately position itself between its master and the stranger.(Wikipedia)