("Aaron the Orthodox or Just"), the most renowned of the Abbaside caliphs; succeeded to the caliphate in 786 on the death of his elder brother, El Hádi, and had for grand-vizier the Barmacide Yâhyá, to whom with his four sons he committed the administration of affairs, he the while making his court a centre of attraction to wise men, scholars, and artists, so that under him Bagdad became the capital of the civilised world; his glory was tarnished by one foul blot towards the end of his reign, and that was the massacre out of jealousy of the Barmacide family, members of which had contributed so much to his fame, an act which he had soon occasion to repent, for it was followed by an insurrection which cost him his life; the halo that invests his memory otherwise was, however, more fabulous than real, and history shows him at his best to have been avaricious, resentful, and cruel.