Michael I Cerularius

Michael I of Constantinople (born Michael Cerularius; Greek: Μιχαὴλ Κηρουλάριος, romanized: Mikhaḕl Keroulários; c. 1000 – 21 January 1059) was the Ecumenical Patriarch of Constantinople from 1043 to 1059. His disputes with Pope Leo IX over church practices in the 11th century played a role in the events that led to the Great Schism in 1054.

Source: Wikipedia — https://en.wikipedia.org/wiki/Michael_I_Cerularius