John Doukas (Caesar)

John Doukas
Ιωάννης Δούκας
John Doukas; Ιωάννης Δούκας
Emperor and Autocrat of the Romans ; Kaisar
	Seal of John Doukas as Caesar
Usurper of the Byzantine Empire
Reign	1074
Predecessor	Michael VII
Successor	Nikephoros III
Caesar of the Byzantine Empire
First Reign	c. 1060—1074
Regent	List of Emperors Constantine X Doukas; (c. 1060–1067) ; Michael VII Doukas; (c. 1060–1074) ; Konstantios Doukas; (c. 1060–1074) ; Romanos IV Diogenes; (1068–1074) ; Andronikos Doukas; (1068–1074) ;
Second Reign	1081—1088
Regent	List of Emperors Alexios Komnenos; (1081–1088) ; Constantine Doukas; (1081–1087) ;
Basileopator	c. 1071—1078
Born	c. 1000
Died	c. 1088
Spouse	Irene Pegonitissa
Issue	Andronikos Doukas; Constantine Doukas
Dynasty	Doukas
Father	Andronikos Doukas (not his grandson)

John Doukas (or Ducas) (Greek: Ιωάννης Δούκας, 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 older brother of Emperor Constantine X Doukas. John Doukas was the paternal grandfather of Irene Doukaina, wife of Emperor Alexios I Komnenos.

He was the original owner of Codex Parisinus graecus 2009, i.e. the oldest known and preserved manuscript of De Administrando Imperio written by Emperor Constantine VII Porphyrogenitus, and copied by one of Doukas' scribes, a well-known encyclopedic Byzantine source on foreign nations from the 10th century.