Leo IV reigned five years between two committed iconoclasts, relaxed the persecution of monks, and died at thirty leaving a nine-year-old son and a widow who would undo the family's religious policy.
Leo IV ruled for five years between his father Constantine V, who persecuted the monasteries, and his wife Irene, who restored the icons. He did neither.
He kept the iconoclast position formally but stopped enforcing it harshly, appointed monks to bishoprics, and let the temperature fall — until near the end of his reign, when he moved against courtiers found with icons.
He died at thirty in 780, leaving a nine-year-old heir and a strongly iconophile widow with the regency, which decided the empire's religious direction for the next twenty years.
He was born in 750 to Constantine V and the empress Irene — a Khazar princess, daughter of the khagan, married to seal an alliance against the caliphate, and the source of his byname.
He was crowned co-emperor as a small child in 751, and grew up in the household of the most militarily successful emperor of the century, campaigning with his father against the Bulgars.
In 769 he married an Athenian orphan named Irene, chosen in circumstances the sources do not explain and who was, whatever the process, a convinced venerator of icons married into the family that had outlawed them.
He is a genuinely difficult figure to read because his reign was short and his position was ambiguous, and the iconophile sources that dominate the period cannot decide whether to credit him with restraint or condemn him for heresy.
What the actions suggest is a ruler who inherited a policy he did not much believe in and was unwilling either to enforce or to repudiate — appointing monks as bishops, ending the public humiliations, and leaving the doctrine in place.
The one hard episode is at the end: in 780 a group of courtiers was found with icons and punished, and the sources link it to a rupture with his wife. Whether that represents a change of heart, a reassertion under pressure from the army, or simply a palace quarrel cannot be determined from what survives.
Militarily the reign continued his father's success without his father's intensity. Byzantine forces campaigned in Syria in 778, taking Germanikeia, and beat back Abbasid raids into Anatolia.
On the northern frontier he kept the peace his father's nine Bulgarian campaigns had bought, and he was preparing an expedition against the Bulgars when he died.
His most consequential act was dynastic: in 776 he had his son Constantine crowned co-emperor and made the army and the city swear to recognise no other line, over the objections of his own half-brothers, whose subsequent conspiracies he put down.
The five years matter mostly for what they made possible. By relaxing the persecution without repudiating the doctrine, he left the question open at exactly the moment his death handed the government to Irene.
She restored the veneration of images at the Second Council of Nicaea in 787, seven years after he died, and the iconoclasm his father had entrenched was condemned as heresy within a generation.
A later tradition holds that he died of a fever brought on by wearing a jewelled crown taken from Hagia Sophia — a story with the shape of a moral about sacrilege, and no evidential value whatever.