The Merry Monarch (1842 – after 1859) was a British Thoroughbred racehorse and sire. In a career that lasted from July 1844 to May 1846 he ran four times and won only one race. That race, however, was the 1845 Epsom Derby, in which he recorded an unexpected victory in a chaotic race. After one race in 1846 he was retired to stud where he made no impression as a sire.