American Pit Bull Terrier
Pit bull is a term commonly used to describe several breeds of dog in the Molosser family. Many breed-specific laws use the term "pit bull" to refer to the American Pit Bull Terrier, American Staffordshire Terrier, and Staffordshire Bull Terrier, and dogs with significant mixes of these breeds; however, a few jurisdictions also classify the American Bulldog and the Bull Terrier as a "pit bull".
The American Pit Bull Terrier is the product of interbreeding between terriers and a now-extinct breed of bulldogs to produce a dog that combined the gameness of the terrier with the strength and athleticism of the bulldog. These dogs were initially bred in England, Ireland, and Scotland, and arrived in the United States with immigrants from these countries. In the United States these dogs were used as catch dogs for semi-wild cattle and hogs, to hunt, to drive livestock, and as family companions; starting in the early 20th century, they began to replace the bull terrier as the "dog of choice" for dog fighting in the United States.
The United Kennel Club (UKC) was the first registry to recognize the American Pit Bull Terrier. UKC founder C. Z. Bennett assigned UKC registration number 1 to his own dog, Bennett’s Ring, as an American Pit Bull Terrier in 1898.
American pit bull terriers today successfully fill the role of companion dog, police dog, and therapy dog; however, American pit bull terriers in general have a higher tendency towards dog aggression and constitute the majority of dogs used for illegal dog fighting in the United States.
Much of a dog's temperament relates to it's breed history and genetic inheritance. I won't go too deep into the history of the Pit Bull as there are many good books and websites that cover the origin and history of the breed. It is common knowledge however, that the Pit Bull breed was developed for blood sports: Bull baiting, bear baiting, and later, dogfighting. What is not common knowledge is that in the days of organized dogfighting, the handlers of the combatants were habitually IN THE PIT with the dogs for the duration of the fight.
They were required to pick up and separate the dogs several times while the dogs were in full fight frenzy. Before the fight, the handlers were required to wash each other's dogs, and after the fight, the badly injured dogs were often treated at ringside by strangers. Any dog that attacked or bit a handler (even if it was the other dog's handler) or anyone else at any time was culled, often on the spot, and would never have been bred.