King of waters, Vala of Eru
Ulmo is a title, which means He who pours. He is also known as King of the Sea and Lord of Waters. Ulmo is the god Poseidon in Greek mythology and Neptune in Roman mythology. Ulmo was one of the chief architects of Arda (the world). Ulmo was third in majesty of the Valar, after Manwë and Varda; in other words, he was the third of the Aratar. He was very close to Manwë. Before the creation of Earth (Arda) when the Ainur sang to his father Ilúvatar, Ulmo was the best singer and maker of music. This translates into the fluidity and versatility of water on Earth, blending with air to form clouds, freezing into ice, running on rivers and mixing in with all aspects of life and landscape. The Elves owe their skill in music to the early teachings of Ulmo and recognize his melodies in the running of streams and rivers as well as the beating of the waves on the sea. Ulmo had always distrusted Melkor, and the Dark Lord feared the Sea almost as much as he feared Varda, because neither could be tamed. Ulmo had no dwelling in Valinor, or any permanent dwelling on land as he preferred the deeps of the seas and the rivers. His palace, on the bottom of Vaiya, was called Ulmonan. He was never married, which added to his isolation.
He seldom came to the Councils of Máhanaxar, and only when in great need. He preferred to stay in Arda, not by walking on the land, as his form would fill Man or Elf with great dread. All waters were under his government; bays, rivers and even the waters under the earth. It is through these that he kept in touch with Arda, and thus knew more of the goings on with the Children of Ilúvatar than even Manwë, for it was said he lived in the very veins of the world. He was said to be fearful to look upon to mortal eye, dressed like a giant wave in glittering green armor, blowing his great horns the Ulumúri.
Ulmo's vassal Ossë, and Ossë's wife Uinen were (along with Melian), to the Elves, the best known of the Maiar. Through them Ulmo would learn much of the Elves