Ilúvatar

"Why hast thou done this? Why dost thou attempt a thing which thou knowest is beyond thy power and thy authority? For thou hast from me as a gift thy own being only, and no more; and therefore the creatures of thy hand and mind can live only by that being, moving when thou thinkest to move them, and if thy thought be elsewhere, standing idle. Is that they desire?" - Ilúvatar to Aulë on the creation of the Dwarves

About
Eru Ilúvatar, The One, created the Ainur spirits from his thought (including the Valar of Time), kindling them to life with the Flame Imperishable that is found within his being, then made the three musical Themes of creation. They were Arda Unmarred, Arda Healed, and that which has not yet been sung. The Ainur sang and worked those themes to create the physical Ardas. Within Arda, the Children of Iluvatar came to existence, and both Ainur and the Children learned much. In the future, after the Last Battle, Eru's themes will be played by the Ainur and the other Children of Iluvatar together with true understanding, and the music shall at last take perfect physical form.

History
Ilúvatar is the sole creator of the Flame Imperishable, and hence the only being in the world able to truly create independent life. All beings not created directly by Ilúvatar, (e.g. Dwarves), still need to be blessed by Ilúvatar through the Flame Imperishable in order to be more than mere puppets of their creator. Melkor desired the Flame Imperishable and long sought for it in vain, but failing to find it because it was within Ilúvatar himself, Melkor could only twist that which had already been given life.

Ilúvatar exercised his power within Arda only if completely necessary. He did, of course, create Arda. He also created and awakened Elves and Men. The Dwarves were "adopted" by Ilúvatar in the sense that they were created by Aulë but given sapience by Ilúvatar. Animals and plants were fashioned by Yavanna after themes set out by Ilúvatar in the Music of the Ainur. Ilúvatar also buried Ar-Pharazôn and his men when they landed at the Undying Lands in the year 3319 of the Second Age. He also caused Arda to take a round shape, drowned Númenor, and caused the Undying Lands to be taken "outside the spheres of the earth". When Gandalf died in the fight with the Balrog, it was beyond the power of the Valar to resurrect him: Ilúvatar himself intervened to send Gandalf back.

In the year 2009 of the Fifth Age, Ilúvatar and the remaining Ainur joined the Valar in the Undying Lands for a short time to once more make music similar to that of the Ainulindalë. This music succeeded in bringing the light of the Eldar back to Middle-earth and casting back the oceans that had conquered Númenor and Beleriand. The song reverberated through all of Eä and Arda, bringing back the flat lay of the world globed within the void and re-opening the way from Middle-earth to The Undying Lands. Much has been restored, kingdoms long forgotten have once more been graced with their former beauty.

Eru as the Creator
Elves and Men were created by Eru directly, without delegation to the Ainur, and they are therefore called "Children of Ilúvatar" (Eruhini). The Dwarves were "adopted" by Eru in the sense that they were created by Aule but given sapience. Sapience is the ability of an organism or entity to act with intelligence. Sapience is synonymous with some usages of the term sentient, though the two are not exactly equal: sentience is the ability to sense or feel, while sapience is the ability to think by Eru. Animals and plants were probably fashioned by Ainur after themes set out by Eru in the Music of the Ainur, although this is questionable in cases where animals exhibit sapience, as in the case of Huan. In Tolkien's fictional universe of Middle-earth, Huan was a great Hound. Huan was given by the Vala Orome the Hunter to his friend Celegorm, one of the Sons of Feanor. Huan was as large as a small horse, and accompanied Celegorm on his huntings. When the Nol, or the Eagles in the Lord of the Rings and the Hobbit.

Accomplishments

 * Created Eä and was the architect in the shaping of Arda.
 * Created the Ainur (Valar and Maiar).
 * Created the Elves.
 * Created Men.
 * Allowed the creation of the Dwarves, but kept them frozen until the Elves and Men were awoken, then gave them sapience.
 * Destroyed Númenor and Beleriand by sinking them both beneath the ocean.
 * Cast the oceans off both Númenor and Beleriand in the Fifth Age.