Duke of Medina Sidonia
Duke of Medina Sidonia is a peerage grandee title of Spain in Medina-Sidonia, holding the oldest extant dukedom in the kingdom, first awarded by King John I of Castile in 1380. His father, Henry II of Castile, had an illegitimate son named Enrique de Castilla y de Sousa with Juana de Sousa, but after being made a Duke by his half-brother in 1380, he died in 1404, without a successor. The title then returned to the Crown.
The title of Duke of Medina Sidonia was awarded a second time on February 1445 by King John II of Castile to Juan Alonso de Guzmán, 3rd Count of Niebla.
They were once the most prominent magnate family of the Andalusian region, the best-known of whom, Don Alonso Pérez de Guzmán y Sotomayor, 7th Duke of Medina Sidonia, commanded the Spanish Armada at the end of the 16th century. The defeat at the hands of weather and the English in 1588 brought disgrace to this family. The House of Medina Sidonia traces its descent from Alonso Pérez de Guzmán.
Counts of Niebla, 1369–1445
Dukes of Medina Sidonia, 1445–present
| From | To | Duke of Medina Sidonia |
| 1445 | 1468 | Juan Alonso de Guzmán, 1st Duke of Medina Sidonia |
| 1468 | 1492 | Enrique Pérez de Guzmán y Fonseca, 2nd Duke of Medina Sidonia |
| 1492 | 1507 | Juan Alonso Pérez de Guzmán, 3rd Duke of Medina Sidonia |
| 1507 | 1512 | Enrique Pérez de Guzmán, 4th Duke of Medina Sidonia |
| 1512 | 1549 | Alfonso Pérez de Guzmán, 5th Duke of Medina Sidonia |
| 1549 | 1559 | Juan Alonso Pérez de Guzmán, 6th Duke of Medina Sidonia |
| 1559 | 1615 | Alonso Pérez de Guzmán y Sotomayor, 7th Duke of Medina Sidonia |
| 1615 | 1636 | Manuel Pérez de Guzmán y Silva, 8th Duke of Medina Sidonia |
| 1636 | 1664 | Gaspar Alfonso Pérez de Guzmán, 9th Duke of Medina Sidonia |
| 1664 | 1667 | Gaspar Juan Pérez de Guzmán, 10th Duke of Medina Sidonia |
| 1667 | 1713 | Juan Claros Pérez de Guzmán, 11th Duke of Medina Sidonia |
| 1713 | 1721 | Manuel Pérez de Guzmán, 12th Duke of Medina Sidonia |
| 1721 | 1739 | Domingo José Claros Pérez de Guzmán, 13th Duke of Medina Sidonia |
| 1739 | 1779 | Pedro de Alcántara Alonso Pérez de Guzmán, 14th Duke of Medina Sidonia |
| 1779 | 1796 | José Álvarez de Toledo, Duke of Alba, 15th Duke of Medina Sidonia |
| 1796 | 1821 | Francisco de Borja Álvarez de Toledo, 16th Duke of Medina Sidonia |
| 1821 | 1867 | Pedro de Alcántara Álvarez de Toledo, 17th Duke of Medina Sidonia |
| 1867 | 1900 | José Joaquín Álvarez de Toledo, 18th Duke of Medina Sidonia |
| 1905 | 1915 | José Joaquín Álvarez de Toledo, 19th Duke of Medina Sidonia |
| 1915 | 1955 | Joaquín Álvarez de Toledo, 20th Duke of Medina Sidonia |
| 1955 | 2008 | Luisa Isabel Álvarez de Toledo, 21st Duchess of Medina Sidonia |
| 2008 | present | Leoncio Alonso González de Gregorio, 22nd Duke of Medina Sidonia |