A cross between a Bulldog and a Mastiff, the Bullmastiff was bred to discourage poachers....
Bullmastiffs are a fairly young breed compared to a lot of other dogs. In the 19th century, British people who owned large amounts of land were having problems with poachers, and they were getting pretty tired of it. They wanted a guard dog that was big, fearless, and fast enough to chase a poacher. The Mastiff was fearless and had size down to an art form, but they werent terribly quick. The Bulldog was fast and also fearless, but too small to intimidate others.
So, breeders doubled up on bravery, added some power and speed, and got the sizeable Bullmastiff, who quickly became the perfect guardian. In fact, they did so well, lots of people in England at the time preferred Bullmastiffs over a Mastiff or a Bulldog because of their balanced qualities. Eventually, the Bullmastiff breed made it to the United States. They were recognized by the AKC in 1933.