Sophie of Mecklenburg-Güstrow (Sophia; 4 September 1557 – 4 October 1631) was Queen of Denmark and Norway from 1572 to 1588 as the wife of Frederick II. She was the mother of Christian IV and Anne of Denmark, and served as regent of the duchies of Schleswig and Holstein from 1590 to 1594. Especially noted for her effective management of her extensive dower lands and a large credit operation, which made her one of the wealthiest landowners and financiers of her time, she was an influential political figure in Northern Europe.
The only child of Ulrich III of Mecklenburg-Güstrow and Elizabeth of Denmark, Sophie married her first cousin Frederick in 1572, aged fourteen. Their union is widely described as unusually affectionate for the period. As queen, she maintained her own household and patronages and pursued interests in natural philosophy, astrology, alchemy, chemistry and iatrochemistry. She supported scholars including Anders Vedel and Tycho Brahe, whom she visited on Ven in 1586 and later. She did not, however, exercise formal political power during the reign of her husband. Following Frederick’s death in 1588, Sophie sought to lead the regency for the underage Christian IV, bringing her into conflict with the Council of the Realm. Although she did not prevail in directing the royal regency, she was recognised by the Danish nobility and Emperor Rudolf II as regent in the duchies until 1594, after which she withdrew to her dower lands, consisting of Lolland and Falster. From there she continued to intervene in affairs of state through correspondence, credit, and marriage diplomacy, arranging advantageous Protestant alliances for her daughters and for Christian IV with the houses of Stuart, Welf (Brunswick-Lüneburg), Hohenzollern (Brandenburg), Holstein-Gottorp and Wettin (Saxony), often contributing substantial funds for jewellery and dowries herself.
