Fray Diego Morcillo Rubio de Auñón, O.SS.T. (sometimes Diego Morcillo Rubio de Suñón de Robledo) (January 3, 1642, Villarrobledo, Albacete, Spain – 1730, Lima, Peru) was a Spanish bishop in Peru and twice viceroy of the colony, from August 15, 1716 to October 5, 1716 (interim) and from January 26, 1720 to May 14, 1724.
At a young age he entered the Calced branch of the Trinitarian Order in Toledo. He studied theology at the University of Alcalá. In Alcalá King Charles II named him preacher of the royal chamber. He also became examiner (calficador) for the Supreme Council of the Inquisition.
On November 21, 1701, he was named during the papacy of Pope Clement XI as Bishop of the Diocese of Nicaragua and consecrated in 1703 by Juan de Argüelles, Bishop of Panamá. Continuing his ecclesiastical advancement, he was appointed by Pope Clement XI as bishop of La Paz, Bolivia on May 14, 1708, by Pope Clement XI as Archbishop of the Archdiocese of La Plata o Charcas on March 21, 1714, and finally by Pope Innocent XIII as archbishop of Lima on May 12, 1723. While bishop, he was the principal consecrator of Juan de Necolalde, Bishop of Concepción (1716); José Luis Palos Bord, Coadjutor Bishop of Paraguay (1723); José Manuel de Sarricolea y Olea, Bishop of Córdoba (1724); and Pedro Morcillo Rubio de Suñón, Auxiliary Bishop of Lima (1724).