Bull and terrier was a common name for bulldog and terrier crossbreeds of the early 1800s. Other names included half-and-halfs and half-breds. It was a time in history when, for thousands of years, dogs were classified by use or function, unlike the modern pets of today that were bred to be conformation show dogs and family pets.^: 14 Bull and terrier crosses were originally bred to function as fighting dogs for bull and bear baiting, and other popular blood sports during the Victorian era. The sport of bull baiting required a dog with attributes such as tenacity and courage, a wide frame with heavy bone, and a muscular, protruding jaw. By crossing bulldogs with various terriers from Ireland and Great Britain, breeders introduced "gameness and agility" into the hybrid mix.

Little is known about the pedigrees of bull and terrier crosses, or any other crosses that originated during that time. The types and styles of dogs varied geographically depending on individual preferences. Breeders in one area may have preferred a cross with a higher percentage of terrier than bulldog. Some early anecdotal reports indicate that bulldog to terrier was preferred over bull and terrier to bull terrier, which was likely to have resulted in at least half or more bulldog blood. The bull and terrier was never a bona fide breed; rather, it referred to a heterogeneous group of dogs that may include purebreds involving different breeds, as well as dogs believed to be crosses of those breeds. Those crossbreeds or hybrids are considered the forerunner of several modern standardised breeds.

In the mid-1830s, when enforcement of the ban on bull baiting had begun, the popularity of the original purebred bulldogs declined, and a major shift in canine genetics was occurring. The appearance of certain dogs were being altered by crossbreeding to better suit function. Not only were appearances of dogs changing, so was the terminology used to describe various breeds and dog types as recorded in ancient records. Such changes began casting doubts over the bulldog's earliest known ancestors.