Ulmo is the Anuir and the power of Arda, a Valar created by Eru.

    He is the Lord of the Waters and he dwells in all the deep about the Earth or under the Earth.
    (Valaquenta, The Silmarillion)

    He is next in might to Manwë, he loves both Elves and the Men and never abandoned them, not even when they lay under the wrath of Valar.