The Bullmastiff originated in Britain around the mid 1800s when gamekeepers bred the English Mastiff and the (now extinct) Old English Bulldog to create a breed of guard dog to protect large country estates from poachers. Standing a little over two feet tall (from top of shoulder to floor) they can range in weight anywhere from 100 to 130 pounds depending on gender. Bullmastiff's are known not only for their size, strength and speed, but also for their quiet and less-aggressive temperament - for this they became known as the Gamekeeper's Night Dog. If a poacher was detected entering the estate the Bullmastiff could cover short distances quickly, knock the intruder down and hold them there until the Gamekeeper arrived.
In modern times the Bullmastiff is known as the loyal family dog. They require structure and consistency to maintain their good nature, but with proper training and attention they are good with all ages and you will only encounter their guardian side if they sense their loved ones are in danger.
Not to mention they're just plain fun!