Lightbringer is the burning red sword of Azor Ahai, the legendary hero said to have ended the Long Night. The songs tell that he laboured fifty days and fifty nights to forge it, and that it shattered twice in the tempering; at the last he drove the blade through the heart of his beloved wife Nissa Nissa, and her death-cry and her soul together gave the sword its living fire. It is named in prophecy as the weapon of the prince that was promised, who will wake to wield it again when the cold returns.
The blade of legend was lost with the age that made it. In the War of the Five Kings, Stannis Baratheon drew a glowing sword from the flames of a burning sept on Dragonstone and named it Lightbringer at the urging of the red priestess Melisandre, who hails him as Azor Ahai come again. But his sword gives light without heat, and wiser heads name it a glamour and no true wonder.
Status: the sword of legend is lost; the blade Stannis bears is widely held to be a counterfeit.