Baldassare Castiglioni was an important statesman and writer of the High Renaissance. His major work "Il Libro del Cortigiano" (Book of the Courtier - 1528) is a commentary on the qualities of the ideal courtier and lady.
The book was written at the court of the famous Duke Guidabaldo Montefeltro of Urbino, and it is still read and studied today.
Raphael's father was the court painter in Urbino and Raphael grew up there. He undoubtedly knew Castiglioni quite well,
and this portrait depicts that gentleman as an ideal courtier and man of great culture.