What is the name of the ancient sword of Isildur?

The ancient sword of Isildur was Narsil. It was originally wielded by Elendil, Isildur’s father, during the Last Alliance of Elves and Men against Sauron at the end of the Second Age.

Narsil was forged in the First Age by the Dwarf-smith Telchar of Nogrod, one of Middle-earth’s most renowned craftsmen. The blade was said to shine with the light of the Sun and Moon, reflected in its Quenya name, commonly interpreted as “red and white flame.”

When Elendil fell in combat with Sauron, Narsil broke beneath him. Isildur then used the sword’s hilt-shard to cut the One Ring from Sauron’s hand. The broken pieces remained an heirloom of Isildur’s heirs for centuries.

A common mix-up is Andúril: that was not the sword’s original name. The shards of Narsil were reforged in Rivendell for Aragorn before the Fellowship began its quest, and Aragorn renamed the restored sword Andúril, meaning “Flame of the West.”