Eleanor of Toledo (Italian: Eleonora di Toledo (1522 – 17 December 1562), born Doña Leonor Álvarez de Toledo y Osorio, was a Spanish noblewoman who was Duchess of Florence from 1539, after Margaret of Austria. Although Eleanor is often referred to as the Grand Duchess of Tuscany, she predeceased the creation of the Grand Duchy of Tuscany. She is credited with being the first modern first lady, or consort. She served as regent of Florence during the absence of her spouse. Eleanor was born in Alba de Tormes, Salamanca, as the second daughter of the Viceroy of Naples, Don Pedro Álvarez de Toledo, Marquis of Villafranca (Charles V's lieutenant-governor) and Maria Osorio, 2nd Marquise of Villafranca. Her father was the second son of Fadrique Álvarez de Toledo, 2nd Duke of Alba and therefore, the 3rd Duke of Alba was his eldest brother. Eleanor was remembered for her beauty: brunette with hazel eyes, an oval shaped face, sweet and full features of an inherent majestic quality, as evident in her portraits. Eleanor was seen as an incredibly charming bride entering the Medici household. Cosimo was searching for a wife who could help strengthen his political position and had initially asked to marry Margaret of Austria, the widow of Duke Alessandro de’ Medici, who displayed enormous reluctance at the idea (thus serving her father’s own interest and plans for her). The Emperor, not wanting to antagonize Cosimo, offered him one of the daughters of the rich viceroy of Naples. The viceroy agreed, provided Cosimo settled a large amount of money on her as dowry. This marriage was politically beneficial as the Medici were new to their ducal status. Additionally, Eleanor's royal Castilian ancestors and relations with the Habsburgs (Emperor Charles V and Eleanor's great grandmothers were sisters, making them third cousins) provided the Medici with the blue blood they had hitherto lacked and began the process of placing them on a footing with other European sovereigns. Through her father, Eleanor also provided the Medici with a powerful link to Spain, at that time ultimately in control of Florence, so that the marriage offered Cosimo I the opportunity to show sufficient loyalty to and trust in Spain that Spanish troops could be withdrawn from the province. Eleanor married Cosimo I de’ Medici in the spring of 1539 at seventeen years of age. Eleanor was married by proxy on 29 March 1539, and set sail from Naples, 11 June, accompanied by her brother Garcia with seven galleys following. They arrived at Livorno on the morning of June 22. That same morning, Eleonora left for Pisa and halfway through, met Cosimo. After a short stay in Pisa, the ducal couple left for Florence, stopping for a few days at the Poggio a Caiano. July 29 marked the grandiose entrance of Eleonora from the Porta al Prato to the church of San Lorenzo for the official wedding, in a grand and lavish celebration. Eleanor and Cosimo had a long and peaceful married life. Surprisingly for the era's patriarchal double standards, Cosimo was faithful to Eleanor throughout their married life. Both were religious and led their lives accordingly. The ducal couple served as an example of a traditional couple, which served to strengthen Cosimo's various reforms and separate him from association with the former Duke.

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