Túrin's sword. It was previously named Anglachel but, after its reforging in Nargothrond, it became Gurthang. Gurthang, also called "Iron of Death", was aptly named, as it brought about the death of Glaurung. This sword and Túrin's exploits earned him many names, including Blacksword, which was based off of the color of his sword.
Reference: Silmarillion "Of Turin Turambar"