Pope Sixtus IV (or Xystus IV, Italian: Sisto IV; born Francesco da Savona later della Rovere; (21 July 1414 – 12 August 1484) was head of the Catholic Church and leader of the Papal States from 9 August 1471 until his death in 1484.

Sixtus IV's accomplishments as pope included the construction of the Sistine Chapel and the creation of the Vatican Library. A patron of the arts, he brought together the group of artists who ushered the early Renaissance into Rome with the first masterpieces of the city's new artistic age.

Sixtus created the Spanish Inquisition through the Papal bull Exigit Sinceræ Devotionis (1478), and annulled the Pontifical decrees of the Council of Constance. He was noted for his nepotism and was personally involved in the Pazzi conspiracy, a plot to remove the Medici family from power in Florence. He died in August 1484 at the age of 70.

Francesco was a member of the della Rovere family, a son of Leonardo Beltramo di Savona della Rovere and Luchina Monteleoni. He was born in Celle Ligure, a town near Savona.

Mandell Creighton says that Francesco was born of such lowly origin that he lacked a surname and took his from the della Rovere di Vinovo family of Turin when he went there to tutor them. Egmont Lee instead writes that "Leonardo was one of the anziani of Savona in 1413, 1425, and 1427, and had participated in an embassy to Filippo Maria Visconti. Pompeo Litta agrees with Creighton that Francesco took the della Rovere Surname from the della Rovere di Vinovo because he asserts that the Leonardo who was one of the anziani of Savona had also been part of the delegation in 1391 to swear allegiance to the Genovese and Leondardo, father of Francesco, must have been two different people, and that Leonardo "della Rovere" was most likely a poorcloth shearer (cimatore di panni).

At the age of 9, Francesco joined the Franciscan Order under Minorite Giovanni de Pinerolo, an unlikely choice for a political career, and his intellectual qualities were revealed while he was studying philosophy and theology at the University of Bologna, and later University of Padua where he received his licentiate on January 19th, 1434 and his doctorate in 1444. He went on to lecture at Padua and many other Italian universities.

In 1446, Francesco was called to be assistant to the minister General of the Fransican order, Antonio Rusconi, and his successor, Angelo Cristoforo del Toscano, who relied on him extensively. By 1459, Cardinal Bessarion had made Francesco della Rovere his personal confessor, holding him in high regard as to describe him in a letter of introduction on June 18, 1459 to Francesco Sforza as "Uno de li primi e piu reputati del suo ordine". In 1464, della Rovere was elected Minister General of the Franciscan order at the age of 50. In 1467, he was appointed Cardinal by Pope Paul II with the titular church being the Basilica of San Pietro in Vincoli.

Before his papal election, Cardinal della Rovere was renowned for his unworldliness and had written learned treatises, including On the Blood of Christ and On the Power of God.