While their origins are unknown, "spaynels" are mentioned in 14th century writings. It is commonly assumed that they originated in Spain, and Edward of Norwich, 2nd Duke of York in his 15th century work The Master of Game introduces them as "Another kind of hound there is that be called hounds for the hawk and spaniels, for their kind cometh from Spain, notwithstanding that there are many in other countries." The Master of Game was mostly an English translation of an earlier 14th century Old French work by Gaston III of Foix-Béarn entitled Livre de Chasse.
In 1801, Sydenham Edwards wrote in Cynographia Britannica that the "Land Spaniel" is divided into two types: the hawking, springing/springer and the cocking/cocker spaniel. The term cocker came from the dog's use in hunting woodcocks. During the 19th century a "cocker spaniel" was a type of small Field Spaniel; at the time, this term referred to a number of different spaniel hunting breeds, including the Norfolk Spaniel, Sussex Spaniel, and Clumber Spaniel. While there were no Sussex Cockers or Clumber Cockers, there were dogs known as Welsh Cockers and Devonshire Cockers. The Welsh or Devonshire were considered cockers until 1903 when they were recognized by The Kennel Club as the Welsh Springer Spaniel.
Prior to the 1870s, the only requirement for a dog to be classed as a Cocker Spaniel was that it needed to weigh less than 25 pounds (11 kg), although breeders separated the cocker from the King Charles Spaniel which remains a smaller breed of spaniel. This maximum weight limit remained on the Cocker Spaniel until 1900, with larger dogs being classed as Springer Spaniels. The colors of the Devonshire and Welsh Cockers were described by John Henry Walsh under the pseudonym Stonehenge in his book The Dog in Health and Disease as being a deeper shade of liver than that of the Sussex Spaniel. Following the formation of The Kennel Club in the UK in 1873, efforts were made by breeders to record the pedigrees of cockers and springers. In 1892, English Cocker Spaniels and English Springer Spaniels were recognized as separate breeds by The Kennel Club.
There are two dogs which are thought to be the foundation sires of both modern breeds of cocker spaniels. Ch. Obo is considered by breed enthusiasts to be the father of the modern English Cocker Spaniel, while his son, Ch. Obo II, is considered to be the progenitor of the American Cocker Spaniel. Obo was born in 1879, at which point registration as a cocker was still only by size and not by ancestry. He was the son of a Sussex Spaniel and a Field Spaniel. Although Obo was an English dog, Obo II was born on American shores – his mother was shipped to the United States while pregnant. During his lifetime, it was claimed in advertisements that Obo II was the sire or grandsire of nearly every prize winning cocker in America.