Ambrosiaster or Pseudo-Ambrose is the name given to the unknown author of a commentary on the epistles of Saint Paul, written some time between 366 and 384 AD.
This is extremely problematic, though, since it would require Ambrose to have written the book before he became a bishop, and then added to it in later years, incorporating later remarks of Hilary of Poitiers on Romans.
Internal evidence from the documents has been taken to suggest that the author was active in Rome during the period of Pope Damasus, and, almost certainly, a member of the clergy.
[1][3] It was traditionally ascribed to Ambrose, but in 1527, Erasmus threw doubt on the accuracy of this ascription, and the anonymous author came to be known as "Ambrosiaster".
[6] In 1905, Alexander Souter established that Ambrosiaster was also the author of the Quaestiones Veteris et Novi Testamenti, a lengthy collection of exegetical and polemical tractates which manuscripts have traditionally ascribed to Augustine.