In the beginning he simply wished for someone who would listen. He who made his own song of Arda. For ages there were none who could comprehend his vision, and he was alone.
Then came Iluvatars chosen, the Elves, Fresh, and pure as a newly sprouted leaf of the brightest green, and curious as a fledgling bird. Gifted with the song of Arda and yet so beholden to it. They celebrated the music of the world endlessly, reveled in it, but only as a cherished memory. So small were they in spirit and mind that they were unable to hear the melodies of the world as the Valar did.
In them Melkor saw an opportunity. At last he would have his audience, in these folk who remembered the song so sweetly. However, when he appeared to them in all his glorious perfection, and bid them listen, he was rebuffed. But in this, the Valar would not be denied. If they would not submit by choice, there were other ways.
Their dismissal awoke within him a terrible wrath.
He stole them away from their starlit home, taking no heed to their desires, to a place of immeasurable darkness. In the heart of Angband he drenched them in his power drowning them in malice until they knew nothing but his will.
Only when they could remember nothing but his own vision did he release them back into the world, to sow his song through Arda.
Perhaps they hoped to return to their lives, in their freedom, but they had been changed, and Melkors work could not be so easily undone.
He had taken from these elves their most precious light.
Rent it from their very souls
Melkor had remade them, bloated them with malice, and twisted their nature into something unnatural.
The horror of the elves when they were reunited with their kin can hardly be fathomed.
For all could see the vile nature of these beings, so changed from what they once were.
They could only weep for their brethren who could no longer hear the trees speak
Or the rivers babble
Or even the listen to the song of the stars.
In their despair over all that had been lost, they could not bear to speak a name so light as Melkor, for they could no longer see the light in the world.
To them he was a figure wreathed only in fear and suffering.
And thus they named him Morgoth