[3]: 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.

[2][4] 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.

Despite anecdotal misinformation and incorrect visual identification, dog owners, animal shelters, veterinarians and the general public routinely use the term "pit bull" in casual and official papers as though it denotes a single, recognised breed.

[4]: 197–202 Bulldogs of the 1800s were described as having a "round head, short nose, small ears and wide, muscular frame and legs.

[5] The assessment, which analysed a particular group of individual English bulldogs, used DNA rather than pedigrees to confirm that genetic diversity actually still exists.

[10] In the 19th century, the Walsall type was carried by immigrants to the United States, where it served as an important component for the genetic basis of the American Pit Bull Terrier breed, through specimens such as the dog Lloyd's Pilot[11] and the Colby bloodline, strongly combined with Irish strains.

[19] Some believe that the courage of most terriers, both past and present, to bear the bites of badgers and other prey they are meant to corner, dig for, or attack is derived from having a quarter to an eighth of Old English Bulldog ancestry.

From his superior courage when crossed with the Bulldog, as most vermin-terriers are, he has generally been kept for killing vermin whose bite would deter the Spaniel or the Beagle, but would only render the terrier more determined in his pursuit of them.

[25] When blood sports were banned in the early 1800s, breeders continued with their clandestine dog fights in discreet venues, such as basements and warehouses.

A major shift in canine genetics occurred during the Victorian era, at which time the appearance of certain dogs were being actively altered.

The early bulldogs of the 1800s were described as having a "round head, short nose, small ears and wide, muscular frame and legs.

Hink's son recalled, "In short, they became the old fighting dog civilized, with all of his rough edges smoothed down without being softened; alert, active, plucky, muscular, and a real gentleman.

The appearance of the Bull Terrier continued to change over time, and by the 20th century its egg-shaped head had become more prominent, soon to be standardised along with the various colours that had been introduced.

Trusty was purchased by Thomas Pitt, 2nd Baron Camelford and presented to Jem Belcher, a champion prize fighter of England.

The breed of dogs of this description, has been much encourage of late, and held in great estimation, as being more staunch than the terrier, and not too powerful for the badger.

Subsequently, Bulls-eye was introduced in The Adventures of Oliver Twist (1838), presumed to be a bull terrier owned by the villain Bill Sykes.