Иоанн Дука
John Doukas (or Ducas) (, "Iōannēs Doukas") (died c. 1088) was the son of Andronikos Doukas, a Paphlagonian nobleman who may have served as governor of the theme of Bulgaria (Moesia), and the younger brother of Emperor Constantine X Doukas. John Doukas was the paternal grandfather of Irene Doukaina, wife of Emperor Alexios I Komnenos.