The Bullmastiff is a powerful-looking, relatively large dog. The Bullmastiff breed is said to have originated when a Mastiff and a bulldog were interbred. Though there are many breeds of hunting dogs, the Bullmastiff dog breed is unique: it was bred to hunt humans. Specifically, it attacked and immobilized poachers. Today, Bullmastiffs are mostly kept as family pets. In the late 1990s, there was a media fur or around Bullmastiffs in Canada. Which were supposedly dangerous to children. There was even a failed proposal to ban the breed from the country.
Here are the characteristics of the Bullmastiff dog breed as determined by the American Kennel Club's published breed standard.

The Bullmastiff's Behaviour

Recommended for: Family pets, guard dogs

The Bullmastiff is described as fearless yet docile, reliable and eager to please. Yet is important to remember that Bullmastiffs were bred to hunt humans, and so they need to be trained carefully. In particular, Bullmastiffs, like many guard dog breeds, can be a bit overprotective and aggressive toward strangers.
Remember that breed only provides a general clue as to any individual dog's actual behaviour. Make sure to get to know dogs well before bringing them into your home.