Hierarch Isaac (Sahak) Partev, Catholicos of Armenia

Hierarch Isaac, surnamed Partev ("the Parthian" — a family cognomen), was born on September 29, 348 (some sources: 338) in Caesarea of Cappadocia. He held the see of Catholicos of the Armenian Church from 387/388 to 428 — the last Catholicos in direct descent from Hieromartyr Gregory the Illuminator of Armenia.

Together with his disciple, Venerable Mesrop Mashtots, he helped create the Armenian alphabet (c. 405) and organized the translation of the Bible into Armenian (the Old Testament translation was conducted under his direction, completed by the mid-430s). He founded schools; edited and translated the Jerusalem Lectionary (420-423), which laid the foundation of Armenian liturgy. He corresponded with St. Proclus of Constantinople (435), defending Orthodox Christological teaching against the Nestorianism spreading into Armenia. He is known as the "second enlightener of Armenia."

He reposed on September 7, 439, in the village of Blur, Bagrevand region (Western Armenia).

IMPORTANT NOTE ON THE COMMEMORATION DATE: the original stub listed September 20/October 3 — targeted verification established that this is not a genuine commemoration date for St. Isaac but a copy of a template, entirely unsubstantiated date also assigned to three unrelated and unverifiable Russian ascetics with the similar name "Isaaky" (see the separate entries isaaky_cherepovetsky, isaaky_lupand, isaaky_solovetsky) — a clear contamination artifact from the phonetic similarity "Isaac"/"Isaaky." Neither the Armenian nor any known Russian church calendar tradition attests September 20/October 3 for St. Isaac Partev. The Armenian Apostolic Church commemorates him on a movable day (the 2nd Saturday after the start of Great Lent, as well as the 33rd day after Pentecost); a reliable fixed commemoration date in the Russian Orthodox Church calendar was not found during this research — the feast_days field has been left empty to avoid fabricating a date, rather than falsely retaining the contaminated one.