Romanos IV Diogenes (Greek: Ρωμανός Δʹ Διογένης), also known as Romanus IV, was a member of the Byzantine military aristocracy who, after his marriage to the widowed empress Eudokia Makrembolitissa, was crowned Byzantine emperor and reigned from 1068 to 1071. During his reign he was determined to halt the decline of the Byzantine military and to stop Turkish incursions into the Byzantine Empire, but in 1071 he was captured and his army routed at the Battle of Manzikert. While still captive he was overthrown in a palace coup, and when released he was quickly defeated and detained by members of the Doukas family. In 1072, he was blinded and sent to a monastery, where he died of his wounds.
He was senior co-emperor alongside Michael VII, Konstantios and Andronikos.