Anastasius Bibliothecarius (c. 810 – c. 878) was bibliothecarius (literally "librarian") and chief archivist of the Roman Catholic Church and also briefly an Antipope.
Read more about Anastasius Bibliothecarius: Family and Education, Abbot of Santa Maria and Secretary of Nicholas I, Head of The Lateran Archives, Envoy To Constantinople, Continued Influence, Presumed Identification With Antipope Anastasius, Translator and Author