After rendering good service on behalf of the latter in a war with the Arabs in 812, he was summoned in 813 to co-operate in a campaign against the Bulgars. Taking advantage of the disaffection among the troops, he left Michael in the lurch at the Battle of Adrianople and subsequently led a successful revolution against him. Leo justified his usurpation by repeatedly defeating the Bulgars who had been contemplating the siege of Constantinople (814-817).
His vigorous measures of repression against the Paulicians and image-worshippers roused considerable opposition, and after a conspiracy under his friend Michael Psellus had been foiled by the imprisonment of its leader, Leo was assassinated in the palace chapel on Christmas Eve, 820.
Slightly edited from an entry in a 1911 encyclopedia\n