Isaac I Komnenos or Comnenus was Byzantine emperor from 1057 to 1059, the first reigning member of the Komnenian dynasty.

The House of Komnenos, Latinized as Comnenus, was a Byzantine Greek noble family who ruled the Byzantine Empire in the 11th and 12th centuries. The first reigning member, Isaac I Komnenos, ruled from 1057 to 1059. The family returned to power under Alexios I Komnenos in 1081 who established their rule for the following 104 years until it ended with Andronikos I Komnenos in 1185. In the 13th century, they founded and ruled the Empire of Trebizond, a Byzantine rump state from 1204 to 1461. At that time, they were commonly referred to as Grand Komnenoi, a style that was officially adopted and used by George Komnenos and his successors. Through intermarriages with other noble families, notably the Doukas, Angelos, and Palaiologos, the Komnenos name appears among most of the major noble houses of the late Byzantine world.