The story of Rudolph The Red-Nosed Reindeer was written in 1939 by Robert L. May, a copywriter for the Chicago-based Montgomery Ward department stores, as a promotional gift for the store's customers. The stores had bought and distributed coloring books every Christmas and saw writing their own story as a way to save money. Montgomery Ward distributed 2.4 million copies of the Rudolph booklet in 1939. A total of 6 million copies had been given out by the end of 1946, even though wartime paper shortages restricted printing.
~Source: Wikipedia