Short answers, pulled from the story.
Galadriel is a royal Elf created by J. R. R. Tolkien, appearing in The Lord of the Rings, The Silmarillion, and Unfinished Tales. She was a grandchild of both King Finwë of the Noldor and King Olwë of the Teleri. Tolkien described her as "the mightiest and fairest of all the Elves that remained in Middle-earth" after the death of Gil-galad.
The Phial of Galadriel is a magical gift she gave to Frodo Baggins when the Fellowship left Lothlórien. It contains a portion of the light of Eärendil's star. Galadriel's power allowed its light to blind and ward off Shelob, the giant spider, in her lair of darkness.
Galadriel refused the One Ring because she knew its corrupting influence would make her "great and terrible." She accepted that refusing it meant Nenya's power would fade, her people would diminish, and her only escape would be to sail west to Valinor.
Cate Blanchett played Galadriel in Peter Jackson's Lord of the Rings and Hobbit trilogies. Blanchett's Galadriel narrates the prologue of The Fellowship of the Ring. Morfydd Clark later portrayed a younger version of the character in the 2022 television series The Lord of the Rings: The Rings of Power.
Namárië is a poem in Quenya that Tolkien wrote for Galadriel to sing as the Fellowship departs Lothlórien. Donald Swann set it to music using the melody Tolkien himself hummed to him. Tolkien recorded a version of the poem sung in the style of a Gregorian chant, published as part of the song-cycle The Road Goes Ever On.
Scholars have compared Galadriel to Dante's Beatrice and the pearl-maiden from the 14th-century English poem Pearl as celestial guide-figures. Tolkien scholar Marjorie Burns drew parallels with Rider Haggard's immortal heroine Ayesha from his 1887 novel She: A History of Adventure. Tom Shippey argued she represents Tolkien's reconstruction of the dangerous and alluring elf implied by Old English words such as ælfscyne.