Soothsayer (1808–1827) was a British Thoroughbred racehorse and sire best known for winning the classic St Leger Stakes in 1811. Bred and originally trained in Yorkshire he won the St Leger on his third racecourse appearance when still unnamed. He was later sold and trained for the remainder of his racing career at Newmarket where he won a valuable sweepstakes in 1812 and a match race against the Derby winner Phantom in 1813. He later became a successful breeding stallion, siring two classic winners and being the Leading sire in Great Britain and Ireland in 1819. He was later exported to Russia where he died in 1827.

The St Leger Stakes is a Group 1 flat horse race in Great Britain open to three-year-old thoroughbred colts and fillies. It is run at Doncaster over a distance of 1 mile, 6 furlongs and 115 yards, and it is scheduled to take place each year in September.