Gléowine was a minstrel of the King's House of Rohan, who composed an immortalizing song about Théoden and his ancestors after the Battle of the Pelennor Fields. It was said that he never composed another song afterwards. It is described in length in The Lord of the Rings, but only the ending is given.
Out of doubt, out of dark, to the day's rising
he rode singing in the sun, sword unsheathing.
Hope he rekindled, and in hope he ended;
over death, over dread, over doom lifted
out of losss, out of life, unto long glory.
Source: Lord of the Rings, Book 6, Ch. V.