The Sultanate of women (1648–1656) was a period in which the political influence of the Imperial Harem was dominant, as the mothers of young sultans exercised power on behalf of their sons. This was not wholly unprecedented; Hürrem Sultan, who established herself in the early 1530s as the successor of Nurbanu, the first Valide Sultan, was described by the Venetian baylo Andrea Giritti as "a woman of the utmost goodness, courage and wisdom" even though she "thwarted some while rewarding others". But the inadequacy of Ibrahim I (1640–1648) and the minority accession of Mehmed IV in 1646 created a significant crisis of rule, which the dominant women of the Imperial Harem filled. The most prominent women of this period were Kösem Sultan and her daughter-in-law Turhan Hatice, whose political rivalry culminated in Kösem's murder in 1651.