This sword was given to Thingol by Eöl to
staying in Nan Elmoth. The sword was then given to Beleg. After the
reforging for Túrin, it became Gurthang.
This sword was forged of meteoric iron by Eöl the dark elf. In it was left some of his hatred, and Melian the Maia warned of its malice to Beleg, but the warning went unheeded. This sword had no equal in all of time, except one - its twin, Anguirel, stolen from Eöl by his son, Maeglin.
Reference: Silmarillion "Of Túrin Turambar"