
As told by Seppala, Chinook is a type of Sled dog from the 1920's. The Chinook breed isn't really used for racing anymore, but it IS still a breed. And only one of few that was actually created in America! They were established in the early 20th century. They're are only about 500 Chinooks living today.
Arthur Walden, once living in the Alaskan Yukon during the Gold Rush days, developed the Chinook dog breed in Wonalancet, a small village in Tamworth, New Hampshire. He wanted to create a sled dog breed with power, endurance, speed and a friendly nature.
Walden started with breeding a mastiff-type dog named Kim, with a direct decendant of Admiral Peary's famous Greenland Husky lead dog Polaris, Ningo. On January 17, 1917 three pups where born. They were named after Rudyard Kipling's characters in
The Jungle Book - Rikki, Tikki, and Tavi.
Rikki demonstrated what Walden was looking for, and was later renamed "Chinook", in honor of his favourite lead dog had owned in Alaska. Chinook means "warm west wind".
Chinook was a phenomenon of nature, not resembling either of his parents. Chinook was not only an exceptional sled dog, but was good with children. Walden was an excellent showman and
promoter - Chinook became a favorite character of the media at races, winter carnivals and exhibitions around New England in the early 1920's. Not only being a sled dog and a wonderful kid's companion, Chinook was an athlete. He lead the winning team in the First International Dog Derby in Berlin, New Hampshire in 1922 and over the next few years set records for distance covered, loads carried and running time. In 1924 Walden founded the New England Sled Dog Club, which is still operating today. Chinook and Walden led the first dog sled team to the summit of Mount Washington in 1926.

Chinook sired many pups who inherited his coloring, size and general characteristics.
By 1927, both Chinook and Walden were not going to let age keep them from perhaps their greatest adventure. Even though Walden was 56, over the maximum age, he applied for the Byrd Antarctic Expedition. Despite his age, he was given the duties of lead driver and trainer of all the dogs to be used on the expedition.
Training began in the winter months of late 1927 and early 1928 where dogs and drivers were assembled at Walden's Wonalancet Farm. In the harsh conditions of New Hampshire's White Mountains, winter survival gear was also evaluted there. Together the drivers worked for a full year training dogs and testing tents and supplies. Of the 100 dogs trained there, half of them were sired by Chinook.
Sadly, during the expedition in Antarctica, Chinook disappeared on his 12th birthday, January 17, 1929. Some say that he realized he was loosing his command over the other dogs, and just went off to die. Others thought that Chinook had an accident and was lost in the snow. Walden wanted to bury his dear friend and dog in his harness, but Chinook's body was lost in the snow to never be found again. Chinook's death was written in news paper around the world.
Upon Walden's return home, the people of the area wanted to honor him by renaming the road that connected the town of Tamworth with Wonalancet to “Waldens” Road. Walden asked that instead they honor Chinook, and to this day is still called "Chinook Trail".
And thus are the basics of how the Chinook breed came to be, and about the dog who started it all - Chinook himself.
Information gathered from here.