The Pit Bull was developed from the strength and athleticism of the Bulldog and the gameness of the Terriers.  Immigrants brought these early Pit Bulls to America, and farmers and ranchers used them for protection, as catch dogs for semi-wild cattle and hogs, for hunting and driving livestock, and as family companions.  He is a working dog, and is suitable for a wide range of jobs due to his intelligence, high energy, and endurance.  He is used for Search and Rescue, narcotics and explosives detection, border patrol, assistance to the deaf, and as a general service dog.  Pit Bulls have historically been, and are still commonly, used for dog fighting.  Although dog fighting is illegal in the United States, and many other countries, it is still practiced.  Due to the nature of dog fighting, the Pit Bull has the image of a "tough" dog, and can be subjected to severe abuse, and often ends up in the custody of animal control services, where Pits Bulls are routinely killed.  Some jurisdictions in the United States have laws that prohibit the sale or breeding of any dog of the type know as Pit Bull Terrier, or laws requiring muzzling in public.  Advocates of the breed argue that irresponsible or neglectful owners, as well as media sensationalism, are largely to blame for this reputation.
Special Note: The name "Staffordshire Terrier" was adopted by some owners and was recognized by the American Kennel Club in 1936.  Later, the word "American" was added to reduce confusion with its smaller British cousin, the Staffordshire Bull Terrier.  Not all breeders, however, agreed with the standard adopted by the AKC, and continued to use the name American Pit Bull Terrier for their lines.  Much confusion still remains in regards to the Pit Bull Terrier, the American Staffordshire Terrier, and the Staffordshire Bull Terrier.  The American Staffordshire Terrier and the American Pit Bull Terrier are considered to be the same breed in England, although they are considered separate breeds in the United States.