Maeglin (meaning 'of sharp glance') was the son of Aredhel, White Lady of the Noldor, and Eöl, the dark elf who dwelt in Nan-Elmoth. His mother called him Lómion, meaning 'Child of the Twilight'.

He had pale skin, but dark hair and dark, piercing eyes that saw into dark corners and the deep places. He lived in Nan-Elmoth with his parents when he was young, but his mother related to him tales of her own youth, of the sons of Fëanor with whom she would ride in the woods. At midsummer, when Eöl was entertained in the halls of the dwarves in the Blue Mountains, they escaped together to the city of Aredhel's brother Turgon.

When Eöl discovered this, he chased them to the Hidden City, and attempted to kill Maeglin. Aredhel intercepted the javelin he threw, where it caught her shoulder. She was treated immediately, but died the next day as the dart was poisoned.

Maeglin was supposedly more like his mother than his father, but still possessed the darkness of Eöl's line. He lived in his uncle's house, and his desire grew for Turgon's only child, Idril. The desire grew black in his heart.

He was captured by Morgoth, and released only when he betrayed to him the city of Gondolin, and was promised Idril as his prize. In the battle that ensued, many lives were lost, including his own. He was thrown off the wall of the city (just like his father) by Tuor.