HARO, LUIS DE (1599-1661), Spanish diplomat, son of the marquis of Caspio and nephew of the duke of Olivares, whom he succeeded as prime minister in 1643. The disastrous war with France and her allies continued until 1659, when Haro concluded with Mazarin the treaty of the Pyrenees. The terms were hard, and Haro was diplomatically no match for Mazarin, but he brought much-needed peace to Spain, and was rewarded by the elevation of the marquesate of Caspio into a dukedom and the title of "prince of the peace." He died at Madrid on Nov. 26, 1661.