He was the original owner of Codex Parisinus graecus 2009, i.e. the oldest known and preserved manuscript of De administrando imperio of Emperor Constantine VII Porphyrogenitus copied by one of Doukas' scribes, a well-known encyclopedic Byzantine source on foreign nations from the 10th century.
[3] His position as Caesar and his family's influence in the Senate meant that he was behind the opposition of the court officials to the Empress Mother Eudokia Makrembolitissa and her marriage to Romanos IV Diogenes.
The Caesar sent his sons Andronikos and Constantine to capture Romanos IV,[7] who had been released from captivity and thus ensured the sole rule of his nephew Michael VII.
[citation needed] In the meantime, the progress of the Seljuk Turks roused the Byzantine government into action, gathering together an army of mercenaries under the command of Isaac Komnenos.
The Norman mercenaries, led by Roussel de Bailleul, rebelled against the Byzantines, crushed an imperial army, and attempted to establish an independent kingdom in Anatolia.
[15] Fixing his headquarters at Dorylaeum, the two armies met near the bridge over the Zompi River, one of the great lines of communication between Constantinople and the central provinces in Asia Minor.
Betrayed by his Frankish mercenaries and by the shameful retreat of the Asiatic reserves under the command of the future Emperor Nikephoros III Botaneiates, John was defeated and captured together with his son Andronikos.
[15] The victorious mercenaries then proceeded to advance to the shores of the Bosphorus, as a relieving force under John's younger son Constantine disintegrated when its commander suddenly died.