Stefano Borgia (3 December 1731 – 1804) was an Italian Cardinal, theologian, antiquarian, and historian.
Cardinal Borgia belonged to a well known family of Velletri, where he was born, and was a distant relative of the House of Borgia. His early education was controlled by his uncle Alessandro (1682–1764), Archbishop of Fermo. From his youth, Stefano Borgia manifested an aptitude for historical research and a taste for relics of ancient civilizations, a line in which he succeeded so well that, at the age of nineteen, he was received into the Academy of Cortona.
He founded a museum in Velletri, in which, during his whole life, he gathered coins and manuscripts, especially Coptic, and which may be considered as his major undertaking and achievement. Such was his passion for antiquities that he is known to have sold his jewels and precious earthenware in order to secure the coveted treasures and have the description of them printed. Borgia placed his scientific collection at the disposal of scholars, regardless of creed and country, and giving them encouragement and support. Paolino da San Bartolomeo, Adler, Zoëga, Heeren, and many others were among his enthusiastic friends.
Borgia was not left entirely to his chosen field of activity, and was called to fill several important political positions. "He was admitted on all hands to be facile Princeps of the Sacred College."Benedict XIV appointed him Governor of Benevento. In 1770 he was made secretary of the Congregation de Propaganda Fide, an office of which he took advantage to acquire antiquities by the help of the missionaries—a help which proved always forthcoming.