High Quality Content by WIKIPEDIA articles! Gustavus (1818 – after 1842) was a Thoroughbred racehorse that won the 1821 Epsom Derby. Gustavus was the first grey horse to win the Epsom Derby. He raced until he was four years old and was retired to stud in 1823. Gustavus was exported to Prussia in 1836, at the age of 18. Gustavus was not a successful sire.