Leviathan (1823-1846) was a British Thoroughbred racehorse who won 16 of 21 starts before injury prompted his retirement. Imported into Tennessee in 1830, he was the leading sire in North America of 1837, 1838, 1839, 1843 and 1848, and also finished second five times. He was also an important broodmare sire, with modern descendants through the female line including Affirmed, Alydar and Dance Smartly.