The eldest of the seven sons of Feanor in Tolkien's book, The Silmarillion. He was also the lord of their armies after Feanor was slain.
He was captured by Morgoth shortly after his return to Middle-Earth and was held for a long time, chained by one arm to the wall of Angband, until rescued. He fought in various battles, including Nirnaeth Arnoediad and the attack on Elwing's forces, in an attempt to retrieve the Silmarils.
Eventually able to obtain one of the 2 jewels from Morgoth's crown, he found it unbearable to hold and ended up casting it into a volcano before killing himself.
Maedhros was the most tragic of the sons of Feanor, and seems to have been written out of many of their darkest deeds.