"Fawkes is a phoenix, Harry. They burst into flame when it is time for them to die, and then they are reborn from the ashes."
The Valar sat in council. Manwe was the first to speak. "The Age of Man has flowered. But the Secondborn have forgotten us. We must send them a token to remind them of the hope we represent, the hope of Arda Unmarred, and their power to shape their fate beyond the circles of the world.
Manwe chose one of his birds, which had the sweetest voice. Nienna gave the creature her gift of healing tears. Varda reached up to the starry heavens, and plucked Gil-Estel, the Star of Hope, from the night sky. She bathed the bird in the light shining from the fire of the star. Then Eru Iluvatar came into their presence and spoke. "The song this bird will sing is the song of the Ainur, the deep, sorrowful, and beautiful second theme." He breathed into the bird, and gave it the power to regenerate at the end of each life cycle.
The council summoned Olorin. He stood before them humbly, and the Valar spoke as one. "You have been chosen for a great task. In the Third Age you bore the ring of Narya, bringing hope and rekindling the fire in the hearts of those you encountered. Now in the Age of Man, you must perform that same role. If you are willing, you will be reincarnated into a mortal form, one to be born in each time when and where hope is most needed. The bird will be your companion each time, and will aid you." Olorin accepted this charge.
Uncounted years later
A young boy stood before a wise man in an office. The wise man spoke, telling Harry Potter about his pet phoenix Fawkes. "Fawkes is a phoenix, Harry. They burst into flames when it is time for them to die, and then they are reborn from the ashes. Fascinating creatures, phoenixes. They can carry immensely heavy loads, their tears have healing powers, and they are incredibly loyal friends."
Later that year, when Harry would battle the basilisk, Fawkes flew down and sang courage, hope, and strength into his heart. He came out of the Chamber of Secrets tired, but victorious over the serpent.
When Harry had to face Voldemort in their final battle, the song of the phoenix sang in his soul, giving him the strength to fight for everything he held dear.
The dark day had ended, and the sun had risen. Always must the Children of Iluvatar battle with the servants of Morgoth, but the song of the phoenix will never let them give up hope.
