William I, also known as William the Silent because of his cautious attitude, was born in Germany. His parents followed the teachings of Martin Luther and were Protestant, but William changed his religion to Roman Catholic to please the Holy Roman Emperor. The Emperor, Charles V, had liked William, and, in 1555, he made him the commander of his troops stationed at the Empire's border with France.

When Charles V abdicated, his son, Philip II, inherited the western part of the Empire. Philip II was concerned about the spread of the Protestant religion in the Low Countries and was determined to stamp it out by force. William, however, re-converted to Protestantism and led a rebellion against Philip II in 1568.

William tried hard to unite all of the Low Countries in the Protestant faith, but it proved an impossible task. In 1579, he led the seven northern provinces in a break away from the rest and formed a separate league. This league was later to be known as the Dutch Republic. In 1581, Philip II let it be known that he would pay a bounty if William was killed. As a result an assassin struck three years later.