Philip II (21 May 1527 – 13 September 1598), also known as Philip the Prudent (Spanish: Felipe el Prudente), was King of Spain from 1556, King of Portugal from 1580, and King of Naples and Sicily from 1554 until his death in 1598. He was also jure uxoris King of England and Ireland from his marriage to Queen Mary I in 1554 until her death in 1558. He was also Duke of Milan from 1540. From 1555, he was Lord of the Seventeen Provinces of the Netherlands.

The son of Emperor Charles V and Isabella of Portugal, Philip inherited his father's Spanish Empire in 1556 and succeeded to the Portuguese throne in 1580 following a dynastic crisis. The Spanish conquest of the Inca Empire and of the Philippines, named in his honor by Ruy López de Villalobos, were completed during his reign. Under Philip II, Spain reached the height of its influence and power, sometimes called the Spanish Golden Age, and ruled territories in every continent then known to Europeans. Philip led a highly debt-leveraged regime, seeing state defaults in 1557, 1560, 1569, 1575, and 1596. This policy was partly the cause of the declaration of independence that created the Dutch Republic in 1581. Philip finished building the royal palace El Escorial in 1584.

Deeply devout, Philip saw himself as the defender of Catholic Europe against the Ottoman Empire and the Protestant Reformation. In 1584, Philip signed the Treaty of Joinville funding the French Catholic League over the following decade in its civil war against the French Huguenots. In 1588, he sent an armada to invade Protestant England, with the strategic aim of overthrowing Elizabeth I and re-establishing Catholicism there, but his fleet was defeated in a skirmish at Gravelines (northern France) and then destroyed by storms as it circled the British Isles to return to Spain. The following year Philip's naval power was able to recover after the failed invasion of the English Armada into Spain. Two more Spanish armadas unsuccessfully tried to invade England in 1596 and 1597. The Anglo-Spanish war carried on until 1604, six years after Philip's death.Under Philip, an average of about 9,000 soldiers were recruited from Spain each year, rising to as many as 20,000 in crisis years. Between 1567 and 1574, nearly 43,000 men left Spain to fight in Italy and the Low Countries (modern-day Belgium, Luxembourg, and the Netherlands).Philip was described by the Venetian ambassador Paolo Fagolo in 1563 as "slight of stature and round-faced, with pale blue eyes, somewhat prominent lip, and pink skin, but his overall appearance is very attractive. ... He dresses very tastefully, and everything that he does is courteous and gracious." Philip was married four times; all his wives predeceased him.