There are many theories as to the origins of the Newfoundland dog. The main theories are: 1) Newfoundlands are descendents from Viking 'bear' dogs brought over ~1000 AD 2) They are descendents from American black wolves or other native dogs 3) They emerged from the inter-breeding of local dogs and European dogs
English settlers who came to Newfoundland admired the Newfoundland dog for its size, strength, ability to swim, and their gentle temperament. They admired the dogs so much they brought them back to England and bred them with large estate dogs, beginning selective breeding for the modern Newfoundland we see today.
Newfoundland dogs were used as 'ship dogs' in the 18th-19th centuries due to their love of water and natural inclination for saving people. The dogs quickly gained great reputations at sea by saving people who fell overboard, carrying lines to shore when the water was too choppy, and bringing back lost fishing gear. On land, Newfoundland dogs were also used for hauling loads, carting, delivering milk, and as sled dogs.