The Bullmastiff is a large, loyal, and protective companion dog. They are known for their courage and strength, making them an ideal guard dog. They are devoted to their family and make excellent watchdogs, alerting their owners to any potential danger.
From Wikipedia
The Bullmastiff is an English breed of dog of mastiff type and large size, with a solid build and a short muzzle. It was developed as a guard dog in the nineteenth century by cross-breeding the English Mastiff with the now-extinct Old English Bulldog. It was recognised as a breed by The Kennel Club in 1924.