Isaac Komnenos or Comnenus was a notable Byzantine aristocrat and military commander in the 1070s. Isaac played a major role in the rise to the throne of his younger brother, the Byzantine Emperor Alexios I Komnenos, and remained a leading figure in his brother's administration until his death.

Alexios I Komnenos, Latinized Alexius I Comnenus, was Byzantine emperor from 1081 to 1118. Although he was not the first emperor of the Komnenian dynasty, it was during his reign that the Komnenos family came to full power and initiated a hereditary succession to the throne. Inheriting a collapsing empire and faced with constant warfare during his reign against both the Seljuq Turks in Asia Minor and the Normans in the western Balkans, Alexios was able to curb the Byzantine decline and begin the military, financial, and territorial recovery known as the Komnenian restoration. His appeals to Western Europe for help against the Turks was the catalyst that sparked the First Crusade.