Isaac Komnenos or Comnenus (Ἰσαάκιος Κομνηνός, 16 January 1093 – c. 1153) was the third son of Byzantine Emperor Alexios I Komnenos and Empress Irene Doukaina. He was raised to the high rank of sebastokrator by his older brother John II Komnenos in reward for his support, but they later fell out, as Isaac began to covet the throne. He spent most of his life after 1130 in exile.
Isaac was a scholar and patron of learning and the arts. His younger son Andronikos I Komnenos eventually managed to realize Isaac's ambitions, becoming Emperor in 1183–1185, the last of the Komnenos dynasty.
As their father Emperor Alexios neared his death in 1118, Prince Isaac supported his older brother Prince John as heir to the throne. His sister Princess Anna knew he was John's man, and did not include Isaac in her plans to subvert the line of succession and place her husband Nikephoros Bryennios on the throne as a puppet ruler.