Juan Manuel Pérez de Guzmán y Silva (7 January 1579 – 20 March 1636) was a Spanish noble and 8th Duke of Medina Sidonia.
He married in 1598, aged 19, Juana de Sandoval, daughter of the Duke of Lerma, a favourite of Philip III of Spain.
As Captain General of the Spanish Galleys (Galeras de España), he fought against the Barbary pirates and played a role in organising the occupation of their bases at Larache and La Mamora in present-dat Morocco.
Captain General of the Atlantic Ocean (Mar Océano) since 1595, he commanded in 1625, from Jerez de la Frontera, the military operations neutralizing the attack on Cadiz by a Dutch-English Fleet, commanded by Sir Edward Cecil.
In order to encourage her husband when the Portuguese nobility offered him the crown of Portugal, Luisa is known for her phrase: "better Queen for one day, than Duchess all my life".