Short answers, pulled from the story.
Leo Allatius was a Greek scholar, theologian, and keeper of the Vatican Library, born around 1586 on the island of Chios. He converted from Greek Orthodoxy to Catholicism and spent his career in Rome, teaching Greek and studying classics and theology.
Leo Allatius died in Rome on the 18th or the 19th of January 1669; sources disagree on the exact date.
In 1622, Leo Allatius supervised the transport of the Palatinate library, 196 cases holding roughly 3500 manuscripts, across the Alps to Rome using a caravan of 200 mules. The collection, a gift from Maximilian of Bavaria to Pope Gregory XV, was then incorporated into the Vatican Library.
In 1645, Leo Allatius, who had trained as a physician, wrote De Graecorum hodie quorundam opinationibus, a work credited with the first methodical discussion of vampires.
Leo Allatius is best remembered outside scholarly circles for De Praeputio Domini Nostri Jesu Christi Diatriba, an unpublished essay listed in Fabricius's Bibliotheca Graeca. According to an unconfirmed nineteenth-century source, it argues that the rings of Saturn are the prepuce of Jesus.
Leo Allatius was passed over for the position of Vatican librarian, serving instead as librarian to Cardinal Lelio Biscia and then Cardinal Francesco Barberini. In 1661, Pope Alexander VII appointed him custodian of the Vatican Library, a post he held until his death.