Cosmas I was a Patriarch of Constantinople from 1075 to 1081. He crowned the Byzantine Emperor Nicephoros III. He also used his influence to try and convince Nikephoros III to resign as his popularity declined and the empire entered a period of instability. He was deposed by Alexios I Komnenos in 1081 after Cosmas had imposed a penance on Alexios and his family for a riot their supporters has started.