(April 1536 – 10 October 1586), born Pellegrino Rainaldi Danti, was an Italian Roman Catholic prelate, mathematician, astronomer, and cosmographer, who served as Bishop of Alatri (1583–1586).

Over the next dozen years, Danti painted 30 maps of regions of the world (based largely upon published prints by Giacomo Gastaldi, Abraham Ortelius, Gerardus Mercator, and others) upon the cabinet doors of the Guardaroba.

For much of his time in Florence, Danti resided at the convent of Santa Maria Novella, and designed the quadrant and the armillary sphere that appear on the end blind arches of the lower facade of the church in 1572 and 1574, on the right and left respectively.

In late September the following year, Cosimo's son, Grand Duke Francesco de' Medici, compelled Danti to leave Florence.

On account of his mathematical skills, Pope Gregory XIII invited him to Rome, appointed him pontifical mathematician and made him a member of the commission for the reform of the calendar.

This project, begun in early 1580 and completed about 18 months later, mapped the entirety of the Italian peninsula in 40 large-scale frescoes, each depicting a region as well as a perspective view of its most prominent city.

When the pontiff commissioned the architect Domenico Fontana to repair the Claudian harbour at Portus, it was Danti who furnished the necessary plans.

[4] While at Rome Danti published a translation of a portion of Euclid with annotations and wrote a life of the architect Jacopo Barozzi da Vignola, preparing also notes for the latter's work on perspective.

Besides the works already mentioned, Danti was the author of Trattato del'uso e della fabbrica dell'astrolabo con la giunta del planifero del Raja; Le Scienze matematiche ridotte in tavole, also a revised and annotated edition of La Sfera di Messer G. Sacrobosco tradotta da Pier Vincenzio Danti.