§ Of the Valar The Silmarillion

Ulmo is the Lord of Waters. He is alone. He dwells nowhere long, but moves as he will in all the deep waters about the Earth or under the Earth. He is next in might to Manwë, and before Valinor was made he was closest to him in friendship; but thereafter he went seldom to the councils of the Valar, unless great matters were in debate. For he kept all Arda in thought, and he has no need of any resting-place. Moreover he does not love to walk upon land, and will seldom clothe himself in a body after the manner of his peers. If the Children of Eru beheld him they were filled with a great dread; for the arising of the King of the Sea was terrible, as a mounting wave that strides to the land, with dark helm foam-crested and raiment of mail shimmering from silver down into shadows of green. The trumpets of Manwë are loud, but Ulmo's voice is deep as the deeps of the ocean which he only has seen.