Atha Ben Harem, or Alhakem ibn Atta, sur-named Mokanna (the veiled), a Moslem impostor, born at Merv, Khorasan, killed about 780. He was by trade a fuller. He pretended to be the embodiment of the living spirit of God, and by his knowledge of philosophy and chemistry was enabled to perform wonders which drew about him a large band of followers. He always wore a veil, declaring that no one could behold his face and live; but the real reason of his doing so is supposed to have been to hide the loss of an eye. The caliph Mahdi having sent an army against him, he shut himself up in the castle of Keh, north of the Oxus, and when no longer able to stand a siege put himself to death. According to some, he set fire to his castle and threw himself into the flames, followed by many of his disciples. Others state that he poisoned himself and his followers; and again others that he threw himself into a cauldron of corrosive acid, in the hope that his complete destruction would follow, causing the belief that he had been removed by divine agency.

Mokanna is the hero of Moore's poem, "The Veiled Prophet of Khorassan."