Why was Frederick William known as the Great Elector?

Frederick William (reigned 1640–1688) was known as the Great Elector primarily because of his success in transforming Brandenburg-Prussia into a significant European state through his political and military leadership.1

He earned this title for several key achievements:

• Military and Administrative Reform: He established a standing army and a centralized bureaucracy, which provided the state with a sound fiscal basis and effective military power. By removing control of finances from provincial estates, he laid the groundwork for Prussian absolutism.12
• Territorial Expansion: Through strategic political and military activities, he acquired eastern Pomerania and several secularized bishoprics, including Halberstadt, Minden, and Magdeburg.1
• Sovereignty: He successfully secured full sovereignty over the Duchy of Prussia, which was confirmed in the Treaty of Oliva in 1660.2
• International Standing: By the end of his reign, he was regarded as the head of German Protestantism, and his state was considered second only to Austria among the principalities of the Holy Roman Empire.1