The name San Diego de Alcala, or Saint Didacus of Alcala, was given to the locality by Captain Sebastian Viscaino upon his arrival from New Spain in November, 1602, in the custom of Spanish explorers, who named the bay and the region in honor of the Saint whose feast day was near.

Didacus, or Diego, was born in 1400, a native of the town of San Nicholas del Puerto, in the diocese of Seville in the Spanish Province of Andalusia. Born to poor but religious parents, Didacus joined a hermit priest who for several years tutored him in devotional exercises. He returned home for a short period of time and soon afterward became a member of the Franciscan Order of Airizafa and there took the habit of a lay brother. The young Franciscan Brother taught Christianity and converted the natives to the Faith in the Canary Islands.

In 1450, Didacus journeyed to Rome with Padre Alonso de Castro to attend the canonization of St. Bernardine of Siena and to join in a celebration proclaimed by Pope Nicholas V. Remaining in Rome for some months, Didacus took charge of the infirmary of the Friary of Ara Caeli, where he was engaged in nursing many sick friars, some of whom were said to have miraculously recovered through his care. He returned to Spain and lived for thirteen years at Alcala in Castile. At Alcala, Didacus was taken ill and died on November 12, 1463. King Phillip II of Spain solicited the Saint's canonization which was decreed in 1588 for the many miracles attributed to him.

Alcala, Spain, has been the seat of a university and a center of learning for centuries. For this reason, the University of San Diego, the Catholic University of the West, is located in an area known as Alcala Park.