The Bullmastiff breed, as it's name suggest, is a combination of the Mastiff, and the Bulldog. It was created in England in the mid 1800's: the only guarding breed to originate in England.

  At the time of it's creation, there were many large estates in England, the owners which frowned upon game in their estates being poached. Gamekeepers were employed to oversee, and protect the game in the estates, and they needed an able assistant; the poachers being a rather dangerous lot since punishment for poaching, was hanging.
  Mastiff's were tried but found to be somewhat slow, and to not have the drive necessary to down , and hold a man. Bulldog's (a quite different type than we see today) were tried, but the Bulldog of that era was very ferocious, and tended to tear the poacher up too much.

  So, crosses were made of the Bulldog, and the Mastiff until a ratio of 60% Mastiff, and 40% Bulldog was achieved. This type of dog, eventually called the Bullmastiff, served the needs of every gamekeeper very well. The dog could track a man in the forest at night; work quietly; and, when close enough. Spring to a hard charge, knocking the poacher down, and holding him to the ground until the gamekeeper arrived. This was no mean feat, since the poachers used every trick, and tool at their disposal to escape, knowing that they faced being hanged for their crimes. The Bullmastiff had to be very brave, and tenacious. More than one suffered death, at the hands of a desperate poacher, or criminal. But, the breed was exactly what the gamekeeper needed, and they did their job well.
  There was a story about a highly trained Bullmastiff named "Thorneywood Terror."  Who toured England with his owner putting on demonstrations for the crowds. The dog's owner would muzzle the dog, and then  give a volunteer, a ten minute head start into the forest. "Thorneywood Terror" never failed to catch, down and hold his man!

  Bullmastiffs are large dogs, although not truly a giant breed. The AKC standard of the breed calls for males, between 25-27 inches in the withers, and 110-130 lbs. Females to be, between 24-26 inches at the withers, and 100-120 lbs. Colors are fawn, red, and brindle; all having a black mask which covers the muzzle, and extends up over the eyes. Brindle is black striping over a base color of fawn, or red. Brindle was the desired color of the original dogs used in England; being it was difficult to see the dog in the forest at night.

‚Äč Typical every day disposition of this breed...

  "Your doorbell rings" get up to answer the door, and your best friend accompanies you to the door to see who's there. If you welcome the person into your home, the dog welcomes them also! If you (Do Not) welcome that person into the home, and they should try to push their way in anyway. The dog will put itself between you, and the visitor. Doing whatever is needed, to change the mind of the person trying to enter uninvited.
History of the Bullmastiff Breed