Saint Didacus of Alcalá (c. 1400–1463), also known as Diego de San Nicolás, was a Spanish Franciscan lay brother celebrated for his humility, charity, and deep spirituality. Born in San Nicolás del Puerto, Andalusia, he initially lived as a hermit before joining the Franciscan Order. Didacus served as a missionary in the Canary Islands, where he was appointed guardian of the Franciscan community on Fuerteventura, an exceptional role for a lay brother. In 1450, he traveled to Rome for the canonization of Saint Bernardine of Siena and remained there to care for friars afflicted by an epidemic, reportedly performing miraculous healings. After returning to Spain, he spent his remaining years in contemplation and service, passing away in Alcalá de Henares on November 12, 1463. Canonized in 1588, he is the patron saint of the city of San Diego, California, which was named in his honor.