(AKC Working Group)
The Bullmastiff is a very powerful, nearly square dog that should appear to be 60% Mastiff and 40% Bulldog. It has a broad, wrinkled head and fairly short, square dark muzzle (about one third the length of the whole head). The nose is black with large nostrils. The dark, medium-sized eyes should have an alert, intelligent expression. The V-shaped, wide-set ears are pendant and dark colored. The teeth should meet in a level or slightly undershot bite. The short back is straight and level between the withers and the loin. The tapering tail is set high and reaches to the hocks. The short, smooth coat comes in brindle, fawn, or red, often with a black mask and black ears.
True to his name, the Bullmastiff originated through crosses between bulldogs and mastiffs, probably as early as the late eighteenth century. The breed was not officially recognized until the 1920s, however. The Bullmastiff was developed as a gamekeeper's dog; his job was to track down, tackle, and then hold down poachers so the gamekeeper could take them into custody. The dogs were fierce and tenacious, but were trained not to bite intruders. When gamekeepers' needs for dogs decreased, the dark brindle dogs so good for night camouflage gave way in popularity to the lighter fawn colorations. Today's Bullmastiff has the same general look as his working ancestors, but he is generally cherished as a reliable, loyal family companion and guardian.
Key Facts:

An alert guard dog. Loyal and devoted, with a good-natured temperament, though he tends to be willful. Docile unless provoked; if provoked he is reputed to be fearless and protective. Needs a firm master and should be thoroughly obedience trained for safety. Be sure to socialize extensively with both people and other dogs at an early age. Despite his guard dog characteristics, the Bullmastiff is considered a loyal and affectionate breed that is relatively mellow.