§ Ainulindalë The Silmarillion

And the Valar drew unto them many companions, some less, some well nigh as great as themselves, and they laboured together in the ordering of the Earth and the curbing of its tumults. Then Melkor saw what was done, and that the Valar walked on Earth as powers visible, clad in the raiment of the World, and were lovely and glorious to see, and blissful, and that the Earth was becoming as a garden for their delight, for its turmoils were subdued. His envy grew then the greater within him; and he also took visible form, but because of his mood and the malice that burned in him that form was dark and terrible. And he descended upon Arda in power and majesty greater than any other of the Valar, as a mountain that wades in the sea and has its head above the clouds and is clad in ice and crowned with smoke and fire; and the light of the eyes of Melkor was like a flame that withers with heat and pierces with a deadly cold.