Balto was an Alaskan husky and sled dog belonging to musher and breeder Leonhard Seppala. He achieved fame when he led a team of sled dogs driven by Gunnar Kaasen on the final leg of the 1925 serum run to Nome, in which diphtheria antitoxin was transported from Anchorage, Alaska, to Nenana, Alaska, by train and then to Nome by dog sled to combat an outbreak of the disease.

Gunnar Kaasen was a Norwegian-born musher who delivered a cylinder containing 300,000 units of diphtheria antitoxin to Nome, Alaska, in 1925, as the last leg of a dog sled relay that saved the U.S. city from an epidemic.