He inherited from his father Basil I an empire that was stronger than it ever had been since the height of the Roman Empire in the 3rd century. However, he and his father hated each other; it is possible that Leo was not Basil's son at all, but the son of his predecessor, Michael III. Basil had almost had Leo blinded as a teenager. In 886, Basil died in a hunting accident, though he claimed on his deathbed that there was an assassination attempt in which Leo was possibly involved.
Leo's surname may be explained by the facts that he "was less ignorant than the greater part of his contemporaries in church and state, that his education had been directed by the learned Photius, and that several books of profane and ecclesiastical science were composed by the pen, or in the name, of the imperial philosopher" (Gibbon). Leo completed work on the Basilica, the Greek translation and update of the law code created by Justinian I, which had been started during the reign of Basil.
Fourth marriage dispute
Leo caused a major scandal with his numerous marriages which failed to produce a legitimate heir to the throne. His first wife, whom Basil had forced him to marry, died in 897, and he re-married Zoë Zaützina, daughter of his counsellor Zaützes, though she died as well in 899. Upon this marriage Leo created the title of basilopator ("father of the emperor") for his father-in-law.
After Zoë's death a third marriage was technically illegal, but he married again, only to have his third wife die in 901. Instead of marrying a fourth time, which would have been an even greater sin than a third marriage (according to the Patriarch Nicholas Mysticus) Leo instead took a mistress, Zoe "of the coal eyes". He was allowed to marry her when she gave birth to a son in 904, but with many penalties, such as the refusal to legitimize his wife as empress.
Leo was a weak-minded ruler, chiefly occupied with unimportant wars with barbarians and struggles with churchmen. He was not as successful in battle as Basil had been. Basil had never lost to the Bulgarians, but in 894 they routed Leo's army. In 895 he was more successful, after first allying with the Magyars, but in 896, without Magyar help, the Byzantines were again defeated. Finally, Bulgarian Symeon, who assumed the title of "Tsar of the Bulgarians and autocrat of the Romaei" secured the independence of his church by the establishment of a patriarchate.
The chief event of his middle reign was the capture of Thessalonica (904) by Muslim pirates (described in The Capture of Thessalonica by John Cameniata) under the renegade Leo of Tripolis. In 907 Constantinople was attacked by the Kievan Rus', who were seeking favourable trading rights with the empire. Leo paid them off, but they attacked again in 911, and a trade treaty was finally signed.
In Sicily and Calabria the imperial arms were unsuccessful, as the Arabs defeated his fleet when he attempted to take back Crete in 912. After this defeat Leo quickly became ill and died. As his son was still a child, Leo's brother and nominal (though powerless) co-emperor Alexander became full emperor.
Probably inspired by stories about the ways of Harun al-Rashid, he would sometimes disguise himself and look for injustice or corruption. On one account, he was even captured by the city guards during one of his investigations. He wanted to know if the city patrol was doing its job appropriately. He was walking alone, disguised, late in the evening without any documentation. He bribed two patrols for 12 nomizmas, and moved on. But, the third city patrol arrested him. When a terrified guardian recognized the ruler in the morning, he was rewarded to his duty, and other patrols were dismissed and punished severely.