The AKC has grouped all of the breeds that it registers into seven categories, or groups, roughly based on function and heritage. Breeds are grouped together because they share traits of form and function or a common heritage. The Cocker Spaniel is the smallest member of the Sporting Group. He has a sturdy, compact body and a cleanly chiseled and refined head, with the overall dog in complete balance and of ideal size. He stands well up at the shoulder on straight forelegs with a topline sloping slightly toward strong, moderately bent, muscular quarters. He is a dog capable of considerable speed, combined with great endurance.
The English Cocker Spaniel is a breed of gun dog. It is noteworthy for producing one of the most varied numbers of pups in a litter among all dog breeds. The English Cocker Spaniel is an active, good-natured, sporting dog  standing well up at the withers and compactly built. It is one of several varieties of spaniel and is the foundation of its American cousin, the American Cocker Spaniel.
American Cocker Spaniels: What's Good About 'Em, What's Bad About 'Em
He is a good working dog, but still loves a cuddle. The English Cocker Spaniel is a medium-sized, compact dog. The head is arched and looks slightly flattened when viewed from the side.
The American Cocker Spaniel should be a sweet-natured, happy, playful dog. And many individuals are. Unfortunately behavioral consultants like myself see an awful lot of American Cockers with neurotic behaviors, including nastiness.