Beren and Luthien

Beren was a mortal man, but Luthien was an immortal elf. Her father, a great elvish lord, in deep opposition to Beren, imposed on him an impossible task that he must perform before he might wed Luthien. This is the kernel of the legend; and it leads to the supremely heroic attempt of Beren and Luthien together to rob the greatest of all evil beings, Melkor, called Morgoth, the Black Enemy, of a Silmaril.