Within the depth-psychology adjacent corpus represented by the Seba library, Nicholas I appears almost exclusively as a figure of ecclesiastical-political history in Francis Dvornik’s exhaustive 1948 study of the Photian Schism. The term designates Pope Nicholas I (858–867), whose pontificate constitutes one of the pivotal axes around which Dvornik organises his revisionist historiography of the ninth-century rupture between Rome and Constantinople. The corpus does not treat Nicholas I as a psychological type or archetypal figure; rather, he functions as an institutional agent whose ideological ambitions — rooted in Gelasian and Leonine theories of papal primacy — drove the confrontation with Patriarch Photius and the Byzantine court. Dvornik’s signal contribution is to displace the image of Nicholas as principled doctrinal guardian and expose instead the political calculation, reactive anxiety, and personal dependence on informants like Theognostos that shaped his escalating campaign against Photius. The tensions foregrounded in the corpus turn on the gap between Nicholas’s claimed universalist jurisdiction and the actual limits of his influence over Frankish bishops, Germanic synods, and the Byzantine Emperor. Nicholas emerges, in Dvornik’s reading, as a papacy in overreach — fear and ambition intertwined — making him a figure of enduring relevance to any study of institutional authority, boundary-testing, and the dynamics of schismatic projection.