The second son of Fëanor, who inherited more of his mother Nerdanel's gentle spirit than any of his brothers. Maglor was famed as a poet and bard, but he took the Oath of Fëanor in Tirion and shared in the woes that came of it.
Maglor followed his father into exile, and saw him perish at the hands of the Balrogs. With the rest of his brothers, he dwelt to the east of Beleriand, and Maglor settled between the Little Gelion and Greater Gelion, the two rivers that came together to form the long Gelion itself. That region - which came to be known as Maglor's Gap - lacked hills or mountains, and so was the place on Beleriand's border that was most open to attack from the north.
All seven of Fëanor's sons survived the Nirnaeth. In the years leading up to that battle, one of the three Silmarils had been recovered from Morgoth's crown, and had come eventually to be held by Dior in Doriath. He would not surrender it to the brothers' claims, and so they assaulted Thingol's ancient kingdom. Celegorm, Caranthir and Curufin all fell in that futile battle. Now only four of Fëanor's sons survived; Maglor, the eldest son Maedhros, and the two youngest brothers Amrod and Amras. After some years had passed, these four came to learn that a Silmaril was held by Elwing at the Mouths of Sirion, and though they restrained themselves for some time, their Oath compelled them to take back the Jewel. So they assaulted their fellow Elves, and Elwing escaped with the Silmaril across the Sea to her husband Eärendil, and together they sailed into the West. That voyage would in time bring about the downfall of Morgoth.
After the destruction of Morgoth, the last two Silmarils were recovered from his Crown. By this time, only Maedhros and Maglor remained of Fëanor's sons, and Maglor came close to repenting the Oath. Wearily, he accompanied his brother in the theft of the Silmarils, but their evil deeds in recovering them meant that the holy Jewels burned their skin. Maedhros in despair leapt into a fiery fissure, and Maglor, the last of the Sons of Fëanor to survive, cast his Silmaril into the Sea. Legend says that he still wanders the shores of the World, singing laments for his despair and regret.
All we know for sure about Maglor's fate is from the closing lines of The Silmarillion, where we're told only that '...he came never back among the people of the Elves' (24, Of the Voyage of Eärendil and the War of Wrath).