Earendil

 Christ I, or The Advent Lyrics are part of the Exeter Book and date from the late 900s AD. Lyrics, in this case, is closer to the literal meaning of "accompanied by the lyre (harp)" of the ancient Greeks, though Anglo-Saxon poets may not have been directly knowledgeable about that. It is a set of 12 antiphons, and #7 contains a reference to "Earendel," the morning star, associated with a much older root referring to the light of dawn, such as in the word aurora. 

It not only suggests Tolkien's Earendil, he makes the connection explicit. 

When first studying A[nglo]-S[axon] professionally (1913) ... I was struck by the great beauty of this word (or name), entirely coherent with the normal style of A-S, but euphonic to a peculiar degree in that pleasing but not 'delectable' language ... it at least seems certain that it belonged to astronomical-myth, and was the name of a star or star-group. Before 1914, I wrote a 'poem' upon Earendel who launched his ship like a bright spark from the havens of the Sun. I adopted him into my mythology in which he became a prime figure as a mariner, and eventually as a herald star, and a sign of hope to men. Aiya Earendil Elenion Ancalima (II 329) 'hail Earendil brightest of Stars' is derived at long remove from Éala Éarendel engla beorhtast. (Personal letter from 1967)

Earendil was thus one of the first puzzle-pieces in Tolkien's Legendarium.  Additional note: Tolkien thought of himself as a philologist, and Lewis describes him as such, both the man himself and his representation as Elwin Ransom in the 1940s sci-fi series. We would call such a person an historical linguist today. Yet there is a distinction: the former studies word roots and tracings in order to understand texts; the latter hews more to an anthropological line and studies historical language relationships in order to understand humans.

You can learn more about the Advent Lyrics at the Anglo-Saxon England podcast. He is also doing a long series on King Canute, which I will summarise far in the future when he has finished.