[Belegorn]

The Ainur were the Powers great and small who worked "to fulfilled the vision which they had seen" [Sil, p. 17] which was Ea. The Maiar were "spirits whose being also began before the World, of the same order as the Valar but of less degree" [p. 23] 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" [p. 12]. So with the Valar, to whom they are "servants and helpers" [p. 23] they saw the vision of Earth and entered in it to bring order.

1 - The Istari or Wizards knew who they were, "though they knew whence they came the memory of the Blessed Realm was to them a vision from afar off, for which (so long as they remained true to their mission) they yearned exceedingly." [UT, p. 407]

2 - Olorin was Gandalf. It is said of Olorin in Valinor, "Wisest of the Maiar was Olorin… his ways took him often to the house of Nienna, and of her he learned pity and patience… he loved the Elves, he walked among them unseen, or in form as one of them, and they did not know whence came the fair visions or the promptings of wisdom that he put into their hearts. In later days he was the friend of all the Children of Illuvatar, and took pity on their sorrows" [Sil, pp. 24-25]. In the downfall of Sauron and evil, "these things were achieved for the most part by the counsel and vigilance of Mithrandir" [p. 378]. He had some of the same qualities as Gandalf and Olorin, counseling the free people with his wisdom and having pity on them. As Gandalf he, "was closest in friendship with the Eldar" just like he used to walk among them as Olorin.

3 - They clad themselves in raiment similar to the Children of Illuvatar or "they may clothe themselves in their own thought, made visible in forms of majesty and dread" [p. 12] and its said of them, "the Valar may walk, if they will, unclad, and then even the Eldar cannot clearly perceive them, though they be present." [Sil, p. 11]

4 - Like the Elves they are bound to Arda. "But this condition Illuvatar made, or it is the necessity of their love, that their power should thenceforward be contained and bounded in the World, to be within it for ever, until it is complete, so that they are its life and it is theirs." [p. 10]

5 - The only diminishment I see is when the Powers put forth their will in the domination of others like Melkor and Sauron. The theme can be changed like when Aule made the Dwarves.