This probably counts as a spoiler for the Silmarillion, if such exist.
The short story: Fëanor was an Elf with too great a spirit. There is such a thing as being too clever, especially in Tolkien's universe. Fëanor made jewels of greater beauty than the world has ever seen, but was also responsible for the first ever genocide.
He was tall, and fair of face, and masterful, his eyes piercingly bright and his hair raven-dark; in the pursuit of all his purposes eager and steadfast.
(from The Silmarillion)
Fëanor was born in the glory days of the Noldor, when many great new things were devised, such as the letters. His real name was Curufinwë, but his mother called him Fëanor. He was the eldest and most beloved of King Finwë's sons, and the only child of Míriel Serindë (whose names mean Sparkling like a jewel and Broideress).
Bearing forth this spirit of fire so exhausted his mother that she could not go on living, but wasted away and went to the halls of Mandos, never to return. Fëanor grew up clever, both in mind and the crafts, but also stubborn and hasty. He designed an alphabet that the Eldar used ever after. As an Elven smith, he was the first who discovered how to create beautiful gemstones.
He married Nerdanel, daughter of Mahtan the smith, and learned more skills from him. Nerdanel bore him seven sons, some of whom took after her in that they had more patience than their father. Not very late after (in Elvish reckoning, at least), Finwë took another wife, Indis the Fair. They had the sons Fingolfin and Finarfin. Fëanor was not pleased. He felt estranged from his family and devoted himself to working and exploring Aman.
The evil Melkor was released from his bonds when he swore that he had reformed. He befriended many Noldor and taught them a great deal, all the while influencing them to do evil. Fëanor hated him from the beginning and gave him the spiteful name Morgoth, but he seems to have been corrupted all the same.
Fëanor's masterpiece was capturing the light of the two trees of Valinor into three wondrous gems, the Silmarils. Such light and splendour was unbearable for the dark Morgoth. In an unguarded moment, he stole the stones and murdered Finwë. Fëanor swore he would take them back or die. To accomplish this he slew many of the Teleri who would not give him their boats and then brought the Noldor north where many of them perished in the ice of Helcaraxë.
Without looking back, Fëanor went towards Angband and challenged Morgoth, despite being heavily outnumbered. He failed in retrieving and was killed by Gothmog, the Balrog lord, his body set in flames by his fiery spirit.
The seven sons of Fëanor,
had taken the oath with their father and were still bound by it to their deaths.