Sophie of Mecklenburg-Güstrow

Sophie of Mecklenburg-Güstrow (Sophia; 4 September 1557 – 4 October 1631) was Queen of Denmark and Norway by marriage to Frederick II of Denmark. She was the mother of King Christian IV of Denmark and Anne of Denmark. She was Regent of Schleswig and Holstein from 1590 to 1594.

The only child of Ulrich III of Mecklenburg and Elizabeth of Denmark, Sophie married her cousin, Frederick II of Denmark, in 1572, and their marriage was remarkably happy. She had little political influence during their marriage, although she maintained her own court and exercised a degree of autonomy over patronages. Sophie developed an interest in astrology, chemistry, alchemy and iatrochemistry, supporting and visiting Tycho Brahe on Ven in 1586 and later. She has later been described as a woman "of great intellectual capacity, noted especially as a patroness of scientists". She became widowed at the age of 31 and in the first few years after Frederick's death, Sophie vigorously endeavoured to consolidate her position of power. However, lacking domestic allies and faced with a power-conscious Danish nobility, this was only partially successful; while she was recognized as regent of Schleswig and Holstein, her efforts to lead the regency council of her underage son came into direct conflict with the Danish Council of the Realm and ultimately proved unsuccessful. In 1594, she retreated to her dower estate, comprising the islands of Lolland and Falster. Despite this setback, Sophie's influence did not diminish throughout her widowhood; on the contrary, she was unwilling to be sidelined from political affairs, and she greatly strengthened her status through enormous and ever-expanding monetary leverage.

Through the skilful management of her vast widowed estate, she amassed an enormous fortune, becoming the richest woman in Northern Europe and the second wealthiest individual in Europe after Maximillian I of Bavaria. From the outset, Sophie displayed exceptional enterprise and determination, implementing wide-scale agrarian reforms to increase the yield and revenue of her estate. Frequently disbursing funds from her "inexhaustible coffers", Sophie financially supported her son, as well as the Council of the Realm, and thereby effectively the entire Danish-Norwegian state. She maintained a large lending business, earning interest, and extending loans to, among others her son Christian IV, her son-in-law King James VI & I, her grandson Duke Frederick Ulrich of Brunswick-Lüneburg, and several other principalities of the Holy Roman Empire. When she died in 1631, James Howell, secretary to the English Ambassador in Denmark, remarked that she was the "richest Queen in Christendom".

Queen Sophie exerted significant political influence both domestically and internationally during her widowhood. She strengthened the Protestant alliances of Denmark through the arrangement of influential marriages for her daughters, often contributing substantial funds for the dowry and jewellery herself. She also conducted extensive correspondence with rulers and nobles across northern Europe, and through her strategic economic dealings, she "[financed] diplomacy and war", as described by historian Merry E. Wiesner-Hanks. Sophie played a crucial role in shaping the foreign relations of Denmark, notably during the Thirty Years' War, influencing peace negotiations and ultimately contributing to the Treaty of Lübeck in 1629.

Some historians, especially earlier ones, have either disregarded Sophie or dismissed her as power-hungry and rapacious. However, 19th-century writers including Ellen Jørgensen considered her a woman of "unparalleled skill" and "indomitable resourcefulness". Recent reassessments recognize her remarkable entrepreneurship as a dowager, and in particular her ability to entrench herself as a pervasive power in the political landscape of late Reformation Denmark and Europe.