J.R.R. Tolkien> The Lord of the Rings / The Silmarillion

Away high in the East swung Remmirath, the Netted Stars, and slowly above the mists red Borgil rose, glowing like a jewel of fire. Then by some shift of airs all the mist was drawn away like a veil, and there leaned up, as he climbed over the rim of the world, the Swordsman of the Sky, Menelvagor with his shining belt. The Elves all burst into song.

-J.R.R. Tolkien
The Fellowship of the Ring

Menelvagor was probably the most beloved of constellations to the Elves and corresponds to today's Orion. It was placed in the sky by Varda to serve as a warning to Melkor and to watch him eternally.

The Elves held it dear because they saw it as a guardian of the World. Symbolically he protects the World from the evils that befall the Children of Ilúvatar and guards it from the return of Melkor. It was one of the most ancient of the constellations, being put in place three ages before the First Age. In The Silmarillion it came to represent Túrin Turambar, who's fate was to face Melkor in the Last Battle. It does not seem to be mere coincidence that Túrin's sword, Anglachel, was forged from meteoric iron.

It, along with The Wain, are the two most important constellations to the Children of Ilúvatar.