William I, Prince of Orange (24 April 1533 – 10 July 1584), also known as William the Silent (Dutch: Willem de Zwijger), or more commonly known as William of Orange (Dutch: Willem van Oranje), was the main leader of the Dutch Revolt against the Spanish Habsburgs that set off the Eighty Years' War (1568–1648) and resulted in the formal independence of the United Provinces in 1581. He was born in the House of Nassau as Count of Nassau-Dillenburg. He became Prince of Orange in 1544 and is thereby the founder of the branch House of Orange-Nassau and the ancestor of the monarchy of the Netherlands. Within the Netherlands he is also known as Father of the Fatherland (Dutch: Vader des Vaderlands). A wealthy nobleman, William originally served the Habsburgs as a member of the court of Margaret of Parma, governor of the Spanish Netherlands. Unhappy with the centralisation of political power away from the local estates and with the Spanish persecution of Dutch Protestants, William joined the Dutch uprising and turned against his former masters. The most influential and politically capable of the rebels, he led the Dutch to several successes in the fight against the Spanish. Declared an outlaw by the Spanish king in 1580, he was assassinated by Balthasar Gérard in Delft in 1584. William was born on 24 April 1533 at Dillenburg castle then in the County of Nassau-Dillenburg, in the Holy Roman Empire (now in Hesse, Germany). He was the eldest son of William, Count of Nassau by his second wife Juliana of Stolberg-Werningerode. William's father had one surviving daughter by his previous marriage, and his mother had four surviving children by her previous marriage. His parents had twelve children together, of whom William was the eldest; he had four younger brothers and seven younger sisters. The family was religiously devout and William was raised a Lutheran. Being a ward of Charles V and having received his education under the tutelage of the Emperor's sister Mary, William came under the particular attention of the imperial family, and became a favorite. He was appointed captain in the cavalry in 1551 and received rapid promotion thereafter, becoming commander of one of the Emperor's armies at the age of 22. This was in 1555, when Charles V sent him to Bayonne with an army to take the city in a siege from the French. William was also made a member of the Raad van State, the highest political advisory council in the Netherlands. It was in November of the same year (1555) that the gout-afflicted Emperor Charles V leaned on William's shoulder during the ceremony when he abdicated his Spanish possessions in favour of his son, Philip II of Spain. In 1559, Phillip II appointed William stadtholder (governor) of the provinces of Holland, Zeeland and Utrecht, thereby greatly increasing his political power. A stadtholdership over Franche-Comté followed in 1561. Although he never directly opposed the Spanish king, William soon became one of the most prominent members of the opposition in the Council of State, together with Philip de Montmorency, Count of Hoorn, and Lamoral, Count of Egmont. They were mainly seeking more political power for themselves against the de facto government of Count Berlaymont, Granvelle and Viglius of Aytta, but also for the Dutch nobility and, ostensibly, for the Estates, and complained that too many Spaniards were involved in governing the Netherlands. William was also dissatisfied with the increasing persecution of Protestants in the Netherlands. Brought up as a Lutheran and later a Catholic, William was very religious but was still a proponent of freedom of religion for all people. The activity of the Inquisition in the Netherlands, directed by Cardinal Granvelle, prime minister to the new governor Margaret of Parma (natural half-sister to Philip II), increased opposition to Spanish rule among the then mostly Catholic population of the Netherlands. Lastly, the opposition wished to see an end to the presence of Spanish troops.

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