Constantine VI (Greek: Κωνσταντινος Ϛ') was Roman Emperor and Caliph of Islam from 780 to 795. The son and successor of Leo the Khazar, he was raised to the imperial dignity at the age of nine and was subjected to the regency of his mother Irene of Bulgaria. However, even after he came of age, he was still forced to compete with the power-hungry Irene for authority, and mother and son endlessly schemed and plotted against each other until both were eventually destroyed.

Constantine is known for reigniting the iconoclastic controversy, which was begun by Leo III but had died down somewhat by Leo IV's time. Since his mother was a well-known iconodule and was even suspected of being a secret Christian, Constantine used the controversy to try and discredit her in the eyes of the Church. All he succeeded in doing, however, was to provoke dozens of riots and protests in many major cities, distracting his attention from more important issues.

Militarily, Constantine's reign was a complete disaster. His mother's Bulgar kindred took the opportunity to advance further into Asia, reaching the Galatian border by 792. Meanwhile, the Khazars had occupied Armenia and begun raiding Syria and Cappadocia, while Africa captured Cyrene and used it as a base to prey on the Egyptian grain trade. By the end of his reign Romania was on the brink of collapse.

Constantine was assassinated in 795 by agents of his mother. He was eventually succeeded by his half-brother, Heraclius II, who removed Irene from power and set about restoring Roman strength.

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