Hierarch Paulinus II of Aquileia

SIGNIFICANT HONEST CAVEAT: unlike typical "undivided-church" Western saints added to the ROC calendar (e.g., Patrick of Ireland), Paulinus of Aquileia is venerated as a saint EXCLUSIVELY in the Roman Catholic Church. The Orthodox Encyclopedia (pravenc.ru) itself tags him "св. (western commemoration Jan 11)" — a notation used precisely for Western saints NOT included in the Orthodox calendar. He is absent from the list of 15 ancient Western saints approved by the ROC Synod on March 9, 2017. Moreover, at the synod of Cividale/Friuli (796–797), which he himself convened, Paulinus personally secured the formal inclusion of the Filioque in the Creed as a doctrinal weapon against Adoptionism — making him one of the key promoters of that teaching in the Latin West, directly at odds with the "impeccable Orthodox confession" criterion the Synodal Commission applies when reviewing Western saints. Only local devotion is documented, at a Moscow Patriarchate parish in Udine, Italy.

Paulinus II of Aquileia (c. 726 – January 11, 802) was Patriarch of Aquileia from 787, a theologian, poet, and leading figure of the Carolingian Renaissance. Born in the Lombard duchy of Friuli, he taught grammar at Cividale before Charlemagne recruited him around 776 to the Palace School at Aachen, working alongside Alcuin. In 787 Charlemagne appointed him Patriarch of Aquileia.

He was a leading opponent of the Adoptionist heresy of Elipandus of Toledo and Felix of Urgell, helping secure its condemnation at the Councils of Regensburg (792) and Frankfurt (794). He organized the peaceful Christianization of the Avars and Alpine Slavs (Carantanians), earning the title "Apostle of the Slovenes."