Arien

Arien by Daniel Govar

Arien was the maiden whom the Valar chose from among the Maiar to guide the vessel of the Sun. In the days of the Two Trees of Valinor, Arien had been the one to tend the tree called Laurelin. It is said that she was mightier than Tilion, the Maia chosen to guide the Moon, because she was a spirit of fire, and able to withstand the heat of Laurelin.

"Too bright were the eyes of Arien for even the Eldar to look on, and leaving Valinor she forsook the form and raiment which like the Valar she had worn there, and she was as a naked flame, terrible in the fullness of her splendor."

― "Of the Sun and Moon and the Hiding of Valinor", The Silmarillion

Etymology

Arien means "Maiden of Sunlight" in Quenya (from árë = "sunlight" and -ien = feminine suffix).

Since Arien is connected to the daisy (corruption of day's eye), it's possible that the name comes from árë + hen "eye"

Other Versions of the Legendarium

In earlier writings by Tolkien, Tilion is said to have been in love with Arien, and because he sought her out the Moon was scarred.

In other writings, Morgoth wanted to claim Arien as a wife, and ravished her, upon which she abandoned her body and "died", leaving the Sun to travel through the skies uncontrollably and burning parts of Arda the world. As well, it is stated in other abandoned writings that she was a Maia of Varda. It is not clear if it was Tolkien's intent to keep these elements in The Silmarillion tradition, had he lived long enough to publish it.