John Arnull (1753-1815[1]) was an English flat racing jockey.
Arnull was jockey to the Prince of Wales[2] and notorious gambler Dennis O'Kelly on whose horse, Serjeant, he won the fifth running of the Derby in 1784.
His younger brother, Sam, had won the inaugural running of the race on board Diomed and his son William would win three Derbies.
[4] John was noted for his hardy constitution in the face of the extreme wasting that jockeys undergo to achieve a race-riding weight.
In order to ride one horse for the Prince of Wales, he went eight days eating nothing but apples and "was not injured by it".