Blazers were first bred in Star, Idaho by Neil Hinck - the founding father. He combined the Morgan, American Quarter Horse, American Saddlebred, and the Thoroughbred. Little Blaze was the first Blazer - bred in 1959.
Blazers are bred to be no smaller than 13 hands and no bigger than 15 hands. However, one of my horses (Brisco) is white, has blue eyes, and is about 17 hands. He is a blazer, he just can't be registered as one because Blazers technically cannot be white, or blue-eyed.