Old English Bulldog
It is believed all dogs that are now classified as pit bulls descend from the British bull and terrier, which were first imported into North America in the 1870s. The bull-and-terrier was a type of dog developed in the United Kingdom in the early 19th century for the blood sports of dog fighting and rat baiting, it was created by crossing the ferocious, thickly muscled Old English Bulldog with the agile, lithe, feisty Black and Tan Terrier. The aggressive Old English Bulldog, which was bred for bear and bull baiting, was often also pitted against its own kind in organised dog fights, but it was found that lighter, faster dogs were better suited to dogfighting than the heavier Bulldog. To produce a lighter, faster more agile dog that retained the courage and tenacity of the Bulldog, outcrosses from local terriers were tried, and ultimately found to be successful.