J.R.R. Tolkien>
The Silmarillion
'If none can release us,' said Maglor, 'then indeed the Everlasting Darkness shall be our lot, whether we keep our oath or break it; but less evil shall we do in the breaking.'
Yet he yielded at last to the will of Maedhros, and they took counsel together how they should lay hands on the Silmarils.
-J.R.R. Tolkien
-The Silmarillion
Maglor was the second son of Fëanor and the only one to survive until the Second Age. He quickly swore The Oath of Fëanor along with his brothers in Tirion and thus came under its doom. Maglor was considered the gentlest and less haughtier than his brothers, and was famed as a bard and poet.
After the Noldor fled to Middle-Earth, Maglor settled in Maglor's Gap, a low-lying land between the Ered Luin and Himring, and guarded it from the forces of Morgoth. During the Dagor Bragollach (Battle of the Quick Fire), the Gap was overrun and Maglor fled to his brother Maedhros in Himring. He remained with his brother through the First Age.
Later, Maglor tried to repent of his Oath, but Maedhros persuaded him to help him steal the two remaining Silmarils. In this they were successful, but the Silmarils would not let them be borne by any of the Sons of Fëanor, and Maglor eventually cast it into the Sea.