Junius Spencer Morgan II (1867–1932), son of J. Pierpont Morgan’s sister Sarah, began collecting rare books while he was in his teens and eventually built a fine collection of the ancient Roman poet Virgil’s works. An indifferent financier and ardent bibliophile, Junius became his uncle’s adviser and de facto librarian, exerting an outsize influence on the nature and scale of Pierpont’s acquisitions. It was Junius who guided Pierpont in his en bloc purchases of other collections, conferred with architect Charles Follen McKim during the Library’s design and construction, and—importantly—introduced Pierpont to Belle da Costa Greene, the librarian who would ultimately displace Junius as manager of all matters related to Pierpont’s books and manuscripts.