The mastiff is one of the oldest recognized breeds, and was originally bred as a gamekeeper’s dog to help them catch poachers. Its large, flattened face and mouth enabled it to grab a poacher and hold him in its powerful jaws until the gamekeeper arrived.
The mastiff’s dark mask and sober expression can make it appear unfriendly, and its size can be intimidating. I believe that the perception of these dogs as aggressive is largely due to their appearance. I have always found them to be dependable, amenable and easygoing pets.