According to Unfinished Tales, Grithnir was a man who served the House of Hador.

He and another, Gethron, were sent with Túrin by his mother, Morwen, to find the lands of Doriath. They were to bring the son of Húrin to the gates of Menegroth, for the lands of Dor-lómin had grown dangerous.

Grithnir never made the journey home, for while a guest at Menegroth, he became ill and died.