Don Carlos María Isidro Benito de Borbón y Borbón-Parma was an Infante of Spain and the second surviving son of King Charles IV of Spain and his wife, Maria Luisa of Parma. He claimed the throne of Spain after the death of his older brother King Ferdinand VII in 1833. His claim was contested by liberal forces loyal to the dead king's infant daughter, resulting in the First Carlist War (1833–1840). Don Carlos had support from the Basque provinces and much of Catalonia, but lost the war. His heirs continued the traditionalist cause, fought two more Carlist wars and were active into the mid-20th century, but never gained the throne.

Charles IV was King of Spain and ruler of the Spanish Empire from 1788 to 1808.