"In the beginning the Elder Children of Ilúvatar were stronger and greater than they have since become; [...].And Oromë loved the Quendi (the Elves), and named them in their own tongue Eldar, the people of the stars; but that name was after borne only by those who followed him upon the westward road.
Yet many of the Quendi were filled with dread at his coming; and this was the doing of Melkor. For by after-knowledge, the wise declare that Melkor, ever watchful, was first aware of the awakening of the Quendi, and sent shadows and evil spirits to spy upon them and waylay them. So it came to pass, some years before teh coming of Oromë, that if any of the Elves strayed far abroad, alone or few together, they would often vanish, and never return; and the Quendi said that the Hunter had caught them, and they were afraid. [...] Now Melkor greatly hated and feared the riding of Oromë, and either he sent indeed his dark servants as riders, or he set lying whispers abroad, for the purpose that the Quendi should shun Oromë, if ever they should meet. [...]
But of those unhappy ones who were ensnared by Melkor little is known of a certainty. For who of the living has descended into the pits of Utumno, or has explored the darkness of the counsels of Melkor? Yet it is held true by the wise of Eressëa, that all those Quendi who came into the hands of Melkor, before Utumno was broken, were put there in prison, and by slow arts of cruelty were corrupted and enslaved; and thus did Melkor breed the hideous race of the Orcs in envy and mockery of the Elves, of whom they were afterwards the bitterest foes. For the Orcs had life and multiplied after the manner of the Children of Ilúvatar; and naught that had life of its own, nor the semblance of life, could ever Melkor make since its rebellion in the Ainulindalë before the Beginning: so say the wise. And deep in their dark hearts the Orcs loathed the Master whom they served in fear, the maker only of their misery. This it may be was the vilest deed of Melkor, and the most hateful to Ilúvatar."

J.R.R. Tolkien - "The Silmarillion" - Chapter 3 (1977)