Alvin Christian Kraenzlein (December 12, 1876-January 6, 1928) was an American athlete. He was the first sportsman to win four Olympic titles in a single Olympics. As of 2004, he is still the only track and field athlete to have done so in individual events only.

Kraenzlein was born in Milwaukee, and attended the University of Wisconsin and later the University of Pennsylvania, studying to become a dentist. He won his first athletics title in 1897, when he won the 220 y hurdles race at the AAU championships. The next few years he gained many more titles, winning 5 AAU titles in both hurdling and long jump events, and 8 IC4A titles in sprinting, hurdling and the long jump. Kraenzlein was especially noted for his hurdling technique, as he was the first to practice the now common method of taking a hurdle with a straight front leg.

In 1900, Kraenzlein prepared for the Olympics in England, winning the British title in the 120 y hurdles and the long jump before entering the 1900 Summer Olympics in Paris. There, he won four titles: the 60 m, the 110 m hurdles, the 200 m hurdles and the long jump. His victory in the latter event was remarkable, as he beat silver medallist Meyer Prinstein only by a single centimeter. Prinstein's mark had been set in the qualification, and he did not attend the final, because it was held on a Sunday.

Kraenzlein retired from athletics the following year, as the owner of 6 world records, and graduated from university. After being a dentist for some years, he became a track coach. He was coach the team of the University of Pennsylvania when he died of a heart disease in Wilkes-Barre, Pennsylvania.