Casiodoro de Reina or de Reyna (c. 1520 – 15 March 1594) was a Spanish theologian who (perhaps with several others) translated the Bible into Spanish.
Reina was born about 1520 in Montemolín in the Province of Badajoz. From his youth onward, he studied the Bible.
In 1557, he became a monk of the Hieronymite Monastery of St. Isidore of the Fields, outside Seville (Monasterio Jerónimo de San Isidoro del Campo de Sevilla). Around then, he had contact with Lutheranism and he became an adherent of the Protestant Reformation. He fled with about a dozen other monks when they came under suspicion by the Spanish Inquisition for Protestant tendencies. He first turned to John Calvin's Geneva but did not find the atmosphere of doctrinaire rigidity of the Calvinist Church to be welcoming. In 1558, Reina declared that Geneva had become "a new Rome" and left.
Reina travelled in 1559 to London, where he served as a pastor to Spanish Protestant refugees. However King Philip II of Spain was exerting pressure for his extradition.
In Seville, in April 1562, the Inquisition made an auto-da-fé in which an effigy of him was burned. The works of Reina and his colleagues were placed in the Index of prohibited books and he was declared a "heresiarch" (leader of heretics).
About 1563 Reina went on to Antwerp, where he became associated with the authors of the Polyglot Bible. In April 1564 he went to Frankfurt, where he settled with his family.