Byzantine emperor who shared the imperial throne with his son-in-law Constantine VII and exercised all real power from 920 to 944. Romanus was admiral of the Byzantine fleet on the Danube when, hearing of the defeat of the army at Achelous (917), he resolved to sail for Constantinople. Soon after the marriage of his daughter Helena to Constantine he was crowned colleague of his son-in-law. His reign was terminated by his own sons, Stephen and Constantine, who in 944 compelled him to become a monk.