Alessandro Farnese (5 October 1520 – 2 March 1589), an Italian cardinal and diplomat and a great collector and patron of the arts, was the grandson of Pope Paul III (who also bore the name Alessandro Farnese), and the son of Pier Luigi Farnese, Duke of Parma, who was murdered in 1547. He should not be confused with his nephew Alessandro Farnese, Governor of the Spanish Netherlands, grandson of Emperor Charles V and great-grandson of Pope Paul III.
Born at the family castle at Valentano in Tuscany (current province of Viterbo), the son of Pierluigi Farnese, who was the son of Cardinal Alessandro Farnese (Pope Paul III); and Girolama Orsini, daughter of Ludovico Orsini, seventh Conte di Pitigliano, and Giulia Conti. They were married in Rome on August 6, 1519. Young Alessandro studied at Bologna along with his cousin, Guido Ascanio Sforza di Santa Fiora. He was a member of the Collegio Ancarano, which had been founded in the 15th century by Petrus de Ancarano de nobilibus de Farnesino provinciae Patrimoniae B. Petri in Tuscia, for students specializing in legal studies.
On 18 December 1534, at the age of 14, he was appointed Cardinal Deacon of the Title of Sant'Angelo in Pescheria by his grandfather Paul III, who had been elected to the papacy two months previously. On August 11, 1535, he was appointed Abbot Commendatory of the Abbey of Tre Fontane on the Via Ostiense, a position he held until 1544. In 1535, he was also appointed Abbot commendatory of S. Étienne de Caën.