Mastiff

The Mastiff, also called the English Mastiff, is a large breed of dog. They have a rectangular body, thick muscles and a massive head with a wrinkled forehead. They stand from to at the shoulder and typically weigh between and . The Mastiff is one of the largest breeds of dogs who can outweigh many full-grown men. They can be gentle with family members but are also excellent guard dogs.
History.
The early Mastiff was called a molosser or molossus. Genetics and breeding dogs to get certain characteristics was unknown then. In 350 BC, Aristotle wrote that the ancestor of the Mastiff was the Molosser. These were the war dogs and guard dogs kept by the Molossoi people, an ancient Greek tribe. Today the two names are often used to mean the same group or family of dogs. For example, the modern St. Bernard is sometimes described as a mastiff and sometimes as a molosser type.
Mastiff or Molosser breeds.
While the Mastiff is a recognized breed, there are also a number of working dog varieties that are closely related to the Mastiff. Many prefer to class them as molosser breeds so as not to confuse them with the Mastiff dog breed. Currently there are about 14 different breeds in the molosser/mastiff family of dogs that are bred from or have a common ancestor with the Mastiff. These include the:
There are also a large number of dog breeds not called molossers or mastiffs, but are related to them. Some of these include the:
The list includes many more.
Training and temperament.
When training a Mastiff, it is important to recognize they have a certain personality type that needs additional time and patience to learn things. A Mastiff is a very relaxed dog and takes his or her time in doing a task. Owners call this the "Mastiff tempo". A Mastiff can't be trained the same as a Border Collie. In temperament, a modern Mastiff is a patient, sweet-tempered family guardian and companion. Gentle training works best. It is important to start that training early in puppyhood. They are a dog of tremendous size and strength and owning a Mastiff is a large responsibility.
Mastiffs are very predictable when they are facing a threat to their family. If an owner and another person act in a threatening way, the Mastiff will usually get between them to protect its owner. This is hard for the other person to miss and usually results in a cooling down of a heated discussion. But, if the situation does get worse, the Mastiff will usually growl or snarl at the other person as a warning. 
Early socialization is important so the Mastiff knows who belongs in the house and who does not. For example, if a Mastiff puppy sees strangers coming and going all the time, they tend to see this as normal and might not recognize an intruder if they see one. However, a properly trained and socialized Mastiff will usually corner a burglar or intruder. Unless the intruder does something foolish, like try to hurt the dog, he or she will probably not be hurt.