Captain of Morgoth
The Captain of Morgoth was present at the Nirnaeth Arnoediad or Battle of Unnumbered Tears as the leader of the host from Morgoth that assailed Fingon at Eithel Sirion.
He most probably perished in the charge of Elves initiated by Gwindor and joined by the host of Fingon. This charge swept away and destroyed the evil host and passed on to Angband.
The Captain most likely had instructions from Morgoth to ensure Fingon's force was brought to battle as early as possible so they could not have the opportunity to outflank Morgoth's main army.
It is not know whether the Captain of Morgoth was Orc, Troll or Balrog.