In January 1925, a diphtheria outbreak threatened the remote town of Nome, Alaska, after winter ice cut off regular supply routes. Norwegian musher Gunnar Kaasen and his lead dog Balto completed the final leg of an emergency 674-mile relay, delivering life-saving diphtheria antitoxin to the city and helping halt the epidemic before it spread further. Known as the Serum Run to Nome, the mission involved 20 mushers and more than 150 sled dogs racing through brutal Arctic conditions in subzero temperatures. Although Kaasen and Balto became the most famous finishers, the success of the relay relied on every participant—especially musher Leonhard Seppala and his lead dog Togo, who covered the longest and most dangerous stretch. The story later inspired the animated film Balto, which introduced the event to a new generation, though it simplified many historical details.(Historic Vids)