He was born in Aegina, in Greece, and was a deacon of Hagia Sophia before his ascension, after Michael II of Constantinople abdicated.
[1] Cosmas II reigned during the rule of Byzantine emperor Manuel I Komnenos.
[3] The exact reasons for the conviction and deposition of Cosmas II are not clearly established; perhaps he was the victim of political intrigue.
[4] It is clear however that Emperor Manuel I intervened directly in forming the Synod that deposed Cosmas II, interviewing personally those who accused him, and testing Cosmas II directly on his opinions of the heretical Niphon.
[5] This affair is typical both of the doctrinal controversies common in the reign of Manuel I and also of the Emperor's readiness to become actively involved in them.