The name Ahasuerus is applied to a Babylonian official to a book of scripture that was first pronounced canonical at what council?
Ahasuerus:  The same name is also applied uncertainly to a Babylonian official (or Median king) noted in the Book of Tobit. Book of Tobit: The Book of Tobit ( ; from the Greek: Τωβίθ "Tōbith" or Τωβίτ "Tōbit", itself from Hebrew: טובי‎ ‎ "Tovi" "my good"; Book of Tobias in the Vulgate from the Greek Τωβίας "Tōbias", itself from the Hebrew טוביה Tovyah "Yah is good") is a book of scripture that is part of the Catholic and Orthodox biblical canon, pronounced canonical by the Council of Hippo (in 393), Councils of Carthage of 397 and 417, Council of Florence (in 1442) and confirmed for Roman Catholics by the Council of Trent (1546).
Council of Hippo