Which horse was the first to win the American Triple Crown of horse racing?

Sir Barton became the first Triple Crown winner when it won the Kentucky Derby, Preakness Stakes, and Belmont Stakes in 1919. The horse was ridden by Johnny Loftus, a famous jockey of the time who was later inducted into the Horse Racing Hall of Fame.

Interestingly, the dates of the races were much different back then, and Sir Barton won the Preakness only four days after winning the Derby. It then won both the Withers Stakes and the Belmont Stakes, making four races won in just 32 days; in fact the horse won the first three races in just two weeks. Nowadays the Preakness is run two weeks after the Derby, and the Belmont three weeks after the Preakness - for a five week time period in which winning horses rarely compete in any other races.

After retiring from racing, Sir Barton was actually purchased by the U.S. Army and used as both a military mount and a breeding stallion, and then died from colic in 1937 on a ranch in Wyoming.

So far only twelve horses have won the Triple Crown, with Sir Barton being the first, and the most recent being American Pharoah in 2015. American Pharoah's win ended the longest drought in Triple Crown history - 37 years, as the previous Triple Crown winner was affirmed in 1978.