After Melkor’s defeat, his avatāra Mairon gradually rallied his other dark servants, and during the Treta Yuga built a new power base for himself in the land of Mordor. Mordor was built in imitation of Angband, though it was not nearly as strong. Mairon lacked the raw power and wrath of his master, but he was far more cunning, and seduced many to his allegiance with promises. With the remaining Elves too weak to counter him after the destruction of Beleriand, Mairon spread his control across large portions of Middle-earth during the Treta Yuga, which became known as the Dark Years. However, Mairon always remained faithful in his allegiance to Melkor; as Mairon expanded his empire into new lands, with it he would also spread a cult devoted to Melkor-worship, promising that one day he would return from the Void. Temples dedicated to Melkor were built by Mairon’s servants throughout Rhûn and Haradwaith, where human sacrifice was practiced.
Eventually, Mairon even managed to convince the King of the Númenóreans to his allegiance, and the Cult of Melkor spread throughout the island until only a few of the Faithful remained, led by Elendil. Mairon became very powerful by converting Ar-Pharazôn to the worship of Melkor, establishing a Cult in which it was only natural that, as Melkor’s foremost former disciple, he became high priest. This cult exploited the Númenórean fear of death by claiming that obedience to Melkor would grant the Men of Númenor immortality. Mairon used this religion among his means of encouraging Ar-Pharazôn’s invasion of Valinor, which resulted in the destruction of Númenor by Ulmo. Númenor was then destroyed, but the Cult of Melkor is the de facto religion of Atrosoudn (B. Anvil of Tomorrow, S. Mordor)
The Worship of Melkor is the religion of the Black Númenóreans as well as most of the inhuman species. Melkorism teaches that Arda is a form of play (Maya), subverted by the demiurgic Manwe and his sycophants. Blinding lies are promulgated solely to entrap the Children of Darkness within the confines of morality so that Manwe might rule over them. The Khilafa of Melkorism is Mairon, a theophany. Those who profess the religion of Melkorism seek the eventual destruction of the blinding lies of Manwe. A return to the unbounded freedom and bliss of the Darkness. Mairon, who has been entrusted with the sublime task of preparing the way for Melkor’s eventual return at the end of days. After the Last Battle, Arda will be remade, and the Children of Darkness will be liberated.
The Temple to Melkor in Númenor are domed with a hole in the top to allow smoke from the fire below to exit as wood and human sacrifices are burned. Mairon, since the downfall of Melkor has had himself worshiped as a god by his subjects. Great champions such as the Witch-king of Angmar are also regarded deities in Melkorism.
The Gospel of Melkor
I am the Elder King: Melkor, first and mightiest of all the Valar, who was before the world, and made it. The shadow of my purpose lies upon Arda, and all that is in it bends slowly and surely to my will. But upon all my foes my thought shall weigh as a cloud of Doom, and it shall bring them down into darkness and despair. Wherever they go, evil shall arise. Whenever they speak, their words shall bring ill counsel. Whatsoever they do shall turn against them. They shall die without hope, cursing both life and death.
Only fools have dared to mock me, and have questioned the power of Melkor, Master of the fates of Arda. Therefore with my eyes my servants shall see, and with my ears my slaves shall hear, and nothing shall be hidden from them. Though my enemies have learned the lessons of Aman’s masters by rote, such childish lore will not help them, now they are all fled away. Beyond the Circles of the World I will not pursue them, for beyond the Circles of the World there is Nothing.
The Apocalypse of Námo
Thus spoke Námo in prophecy, when the Pretender caricatured law in Valinor and the rumour of his word was whispered among all the Elves. When the world is old and the Powers grow weary, then Morgoth, seeing that the guard sleepeth, shall come back through the Door of the Night out of the Timeless Void; and he shall destroy the Sun and the Moon.