Alexander was co-emperor for twenty-six years and sole ruler for thirteen months, in which he dismissed his brother's ministers, refused tribute to Bulgaria and started a thirty-year war.
Alexander was crowned co-emperor as a child in 879 and remained one for thirty-three years, of which twenty-six were under his brother Leo VI, who gave him no authority whatever.
When Leo died in May 912 he became senior emperor and regent for his six-year-old nephew, and used the position mainly to reverse his brother's arrangements: the ministers were dismissed, the patriarch deposed, and his brother's widow expelled from the palace.
He then refused the annual tribute to Symeon of Bulgaria, which restarted a war that ran for the next thirty years. He died thirteen months into the reign.
He was born about 870, the son of Basil I and Eudokia Ingerina, and was made co-emperor in 879 after the death of his eldest brother.
That was the extent of his career. Leo VI, who succeeded in 886, kept him in the purple and out of the government for a quarter of a century, and the sources describe a man who filled the time with hunting, the hippodrome and the company of his own household.
Whether he was as idle as the tradition says or simply had nothing to do is impossible to separate, and it is worth noting the question rather than assuming the answer.
The sources are uniformly hostile and unusually specific, which does not make them right but does make them interesting.
They describe drunkenness, indifference to government, and an interest in pagan divination — including a story that he had a bronze statue in the hippodrome dressed and fed on the advice of soothsayers, in the belief that it was linked to his health.
What is not in dispute is the pattern of the thirteen months: everything his brother had built was undone quickly and with evident personal animus, and nothing was put in its place. He was a man kept from power for twenty-six years who used it, when it came, to settle scores.
He removed Leo's ministers and the admiral Himerios, deposed the patriarch Euthymios and restored Nicholas Mystikos, and expelled the empress Zoe — Constantine VII's mother — from the palace.
The consequential act was foreign. Symeon of Bulgaria sent an embassy in 913 to renew the treaty and the annual payments; Alexander dismissed it and refused the tribute.
Symeon invaded, and the war that followed dominated the next three decades, brought Bulgarian armies to the walls of Constantinople and forced the empire to recognise Symeon as emperor of the Bulgarians. Alexander was dead within months of starting it, and his seven-year-old nephew inherited it.
He is the clearest case in this archive of how much damage a short reign can do, and the Bulgarian war he provoked is the reason the following decade of Constantine VII's minority was as dangerous as it was.
The mosaic in the north gallery of Hagia Sophia, made in his thirteen months and still in place, is the strange survival: a securely identified contemporary portrait of a Byzantine emperor, which is more than most of his far more consequential predecessors left.
He died at the ball-court, and the tradition treats it as divine judgement. It reads more like exhaustion in a man of forty-three who had spent twenty-six years waiting and thirteen months in a hurry.