Isaac I Komnenos (or Comnenus) (Greek: Ισαάκιος A' Κομνηνός) was Byzantine Emperor from 1057 to 1059, the first reigning member of the Komnenos dynasty. During his brief reign he attempted to restore the depleted finances of the empire and the former strict organization of the government.
Isaac was the son of Manuel Erotikos Komnenos, who reportedly served as strategos autokrator of the East under Emperor Basil II, and defended Nicaea against the rebel Bardas Skleros in 978. Manuel's native language was Greek; according to Steven Runciman, he was either Greek or a Hellenized Vlach.
During the disturbed reigns of Basil's seven immediate successors, Isaac by his prudent conduct won the confidence of the army. From 1042 to 1057, he served as commander of the field army in Anatolia. In 1057, after being humiliated by the Emperor, Michael VI, he rebelled in Paphlagonia and joined with the nobles of the capital in a conspiracy against the Emperor. The army proclaimed Isaac emperor on June 8, 1057, and he defeated an imperial army at the Battle of Petroe. A panicked Michael VI attempted to negotiate with the rebels through the famous courtier Michael Psellos, offering to adopt Isaac as his son and to grant him the title of Caesar, but his proposals were publicly rejected. Privately Isaac showed himself more open to negotiation, and he was promised the status of co-emperor. However, during the course of these secret negotiations, a riot in favor of Isaac broke out in Constantinople. With the deposition of Michael VI, Patriarch Michael Keroularios crowned Isaac I emperor on September 1, 1057, taking much of the credit for Isaac's acceptance as monarch.