Tilion was a Maia who guided the vessel that contained Telperion’s last fruit. His story evolves along with Arien’s, the Maia who carried the last fruit of Laurelin in her vessel. In the first versions of the legendarium Tilion was not mentioned yet, but there was a young Maia, Silmo, loved by Irmo, and who would "lay in dreams by the pools of Estë"; he was in charge of watering the roots of Telperion, but he didn’t become the one in charge of the vessel of the Moon. That was Ilinsor, a spirit of the Air, Maia of Varda.1
In the first versions of the legendarium both Trees needed to be watered, and Silpion’s dew was kept in a cauldron named Silindrin. Laurelin was the elder Tree and Urwendi took care of watering it. Tilion only makes his appearance in a later version:
Urien [Arien] was a maiden who had tended the golden flowers in the gardens of Vána, while still joy was in the Blissful Realm, and Nessa daughter of Vána danced on the lawns of never-fading green. Tilion was a hunter from the company of Oromë, and he had a silver bow. Often he wandered from its course pursuing the stars upon the heavenly fields.2
In later versions there is no longer need to water the Trees, and Tilion is in love with Arien:
Tilion was a young hunter of the company of Oromë, and he had a silver bow. He loved Arien, but she was a holier spirit of greater power, and wished to be ever virgin and alone; and Tilion pursued her in vain. Tilion forsook then the woods of Oromë, and dwelt in the gardens of Lorien, sitting in dream beside the pools lit by the flickering light of Sipion.3
The last two versions of the tale are almost the same:
In the days of the Trees Arien had tended the golden flowers in the gardens of Vána, and refreshed them with the bright dews of Laurelin; but Tilion was a young hunter of the company of Oromë, and he had a silver bow. He was a lover of silver, and when he would rest he forsook the woods of Oromë, and went unto Lórien and lay adream by the pools of Estë, in the flickering beams of Telperion; and he begged to be given the task of tending ever the last Flower of Silver.4
We know that the Trees gave a last fruit after Melkor and Ungoliant killed them. The description of the "birth" of last fruit of Telperion is beautiful as it is written in the original Lost Tales version of the story. The final fruit was born seven days after the making of the Sun because the Valar’s sons and daughters (the Maiar), and even a few of the Valar, were distressed because the light of the Sun and the incessant heat was making their eyes hurt, and the plants and flowers wither. So Lórien (Irmo), who was sitting under Silpion (Telperion) trying to get some shadow, started to sing to the dead Tree:
Then Lórien sang to Silpion, saying that the Valar were lost ‘in a wilderness of gold and heat, or else in shadows full of death and unkindly glooms,’ and he touched the wound in the bole of the Tree.
Lo, even as he touched that cruel hurt, a light glowed faintly there as if radiant sap still stirred within….
One only was there at the branch’s end that opening shone of its own light and no mist or a sicold harmed it, but indeed waxing it seemed to suck the very vapours and transform them subtly to the silver substance of its body; and it grew to be a very pale and wondrous glistering flower, nor did even the purest snow upon Taniquetil gleaming in the light of Silpion outrival it, and its heart was of white flame and it throbbed, waxing and waning marvellously. Then said Lorien for the joy of his heart: "Behold the Rose of Silpion", and that rose grew till the fruit of Laurelin had been but little greater, and ten thousand crystal petals were in that flower, and it was drenched in a fragrant dew like honey and this dew was light.5
So, in the first versions of the story, Silmo begs to steer the fruit of Telperion’s car, but is denied. Ilinsor, a Maia of Varda, is given control of the vessel, together with other spirits of the air:
Now Silmo begged to sail upon the oceans of the firmament therein, but he might not, for neither was he of the children of the air nor might he find a way to cleanse his being of its earthwardness as had Urwendi done, and little would it have availed to enter Faskalan had he dared essay it, for then would Rána have shrivelled before him. Manwë bade therefore Ilinsor, a spirit of the Súruli who loved the snows and the starlight and aided Varda in many of her works, to pilot this strange-gleaming boat, and with him went many another spirit of the air arrayed in robes of silver and white, or else of palest gold….6
There was a pool that contained the pale dew that the Rose of the Moon still gave:
Hence was it that a pool was builded hard by the dark southern wall of Valmar, and of silver and white marbles were its walls, but dark yews shut it in, being planted in a maze most intricate about it. There Lorien hoarded the pale dewy light of that fair Rose, and he named it the Lake Irtinsa.7
There is an interesting explanation about the legend of “the man in the moon”:
… an aged Elf with hoary locks stepped upon the Moon unseen and hid in the Rose, and them dwells he ever since and tends that flower, and a little white turret has he builded on the Moon where often he climbs and watches the heavens, or the world beneath, and that is Uolë Kúvion who sleepeth never. Some indeed have named him the Man in the Moon, but Ilinsor is it rather who hunts the stars.8
So who was this Elf? Did he and Ilinsor converse while the latter carries the car of the Moon across the sky? Has the Elf shrunk into a smaller being so he can actually build a home on the Rose? This version was discarded, but it is an interesting insight into the building of Tolkien’s legendarium, what he kept, what he discarded.
There is another explanation for the dark areas on the moon’s surface in The Silmarillion:
But Tilion was wayward and uncertain in speed, and held not to his appointed path; and he sought to come near to Arien, being drawn by the splendour of her beauty, though the flame of Anar scorched him, and the island of the Moon was darkened.9
In the later versions of the story, it is the Moon that comes forth first, and its light welcomes Fingolfin’s host to Middle-earth:
First the Moon came forth, and even as it rose above the darkness in the West Fingolfin let blow his silver trumpets, and began his march into Middle-earth; and the shadows of his host went long and black before them.10
The light surprised Melkor and scared many of his creatures. He sent his servants, spirits of darkness, to assail Tilion, and there was a fight in the skies:
It is told in AAm [Annals of Aman] that ‘Tilion was the victor: as he ever yet hath been, though still the pursuing darkness overtakes him at whiles’, evidently a reference to the eclipses of the Moon.11
The Sun rose soon after, and everything “smoked and glowed like gold.”12 Fingolfin unfurled his blue and silver banners then, and the flowers awoke from the Sleep of Yavanna. Melkor hid his realm with the darkest shadows:
Therefore Fingolfin marched from the North unopposed through the fastness of the realm of Morgoth, and he passed over Dor-Daedeloth, and his foes hid beneath the earth; but the Elves smote upon the gates of Angband, and the challenges of their trumpets shook the towers of Thangorodrim. And Maidros heard them amid his torment and cried aloud, but his voice was lost in the echoes of the stone.13
This is the version published in The Silmarillion:
Isil was first wrought and made ready, and first rose into the realm of the stars and was the elder of the new lights, as was Telperion of the Trees. Then for a while the world had moonlight, and many things stirred and woke that had waited long in the sleep of Yavana. The servants of Morgoth were amazed, but the dark-elves looked up in delight; and it is told that Fingolfin set foot upon the Northern Lands with the first moon-rise, and the shadows of his host were long and black. Tilion had traversed the heavens seven times, and was thus in the furthest East when the vessel of Arien was made ready. Then Anar rose in glory, and the snow upon the mountains glowed as with fire, and there as heard the sound of many waterfalls; but the servants of Morgoth fled to Angband and cowered in fear, and Fingolfin unfurled his banners.14
In the old stories, Tilion’s (Ilinsor’s) final fate is linked to the death of Arien (Urwendi) at Melkor’s hands just before the Dagor Dagorath. This version of their fates was recounted to Gilfanon by Vairë (in The Book of Lost Tales, Vairë is the Elven storyteller of Tol Eressëa, not one of the Valië) in Tol Eressëa15:
'But as for the Ships of Light themselves, behold! O Gilfanon and all that hearken, I will end the tale of Lindo and Vairë concerning the building of the Sun and Moon with that great foreboding that was spoken among the Gods when first the Door of Night was opened. For 'tis said that ere the Great End come Melko shall in some wise contrive a quarrel between Moon and Sun, and Ilinsor shall seek to follow Urwendi through the Gates, and when they are gone the Gates of both East and West will be destroyed, and Urwendi and Ilinsor shall be lost. So shall it be that Fionwë Urion, son of Manwë, of love for Urwendi shall in the end be Melko's bane, and shall destroy the world to destroy his foe, and so shall all things then be rolled away.'16
We can read the last version of the Dagor Dagorath and Arien’s and Tilion’s fates in The Lost Road:
Thus spake Mandos in prophecy, when the Gods sat in judgement in Valinor, and the rumour of his words was whispered among all the Elves of the West. When the world is old and the Powers grow weary, then Morgoth, seeing that the guard sleepeth, shall come back through the Door of Night out of the Timeless Void; and he shall destroy the Sun and Moon. But Eärendel shall descend upon him as a white and searing flame and drive him from the airs. Then shall the Last Battle be gathered on the fields of Valinor. In that day Tulkas shall strive with Morgoth, and on his right hand shall be Fionwë, and on his left Túrin Turambar, son of Húrin, coming from the halls of Mandos; and the black sword of Túrin shall deal unto Morgoth his death and final end; and so shall the children of Húrin and all Men be avenged.17
So as we can see, Tilion’s fate – in his different incarnations – is always linked to Arien’s. In a way, the story of the Lights created by the Valar come full circle, with the deaths of the bearers of the Trees’ last fruits and the rekindle of such Light after Fëanor comes out of the Halls and breaks the Silmarils.