Helm Hammerhand

A specter appears, light green, physical form has robes that cover less arms and legs, which are visibly covered with armor. Additionally, he wears a sinister looking mask that covers the hollow darkness where his face should be, having a mask that has two large horns on both sides of his mask.

...

In the life.

In life, Hammerhand was a powerful but very dark man, who resented fools and did not suffer fools gladly, which made him enemies both outside his kingdom and court, as well as within. As he himself stated, he was a great hunter, having hunted all the beasts of Mordor.

Descent into darkness.

At some point in her life, a powerful warlord known as Siric desired Helm's daughter Berwyn as his wife, and demanded her hand in marriage, which Helm refused. Some time later, Siric ambushed Helm and his daughter as they rode through the forest, and his archers felled him with a volley of arrows at point-blank range and kidnapped his daughter.

Dying from his wounds, Helm was visited on his deathbed on Edoras by Sauron (in the guise of Annatar, his beautiful form) and Celebrimbor; Sauron gifted him a Ring of Power, promising Helm that he would ensure the "safe return of his daughter" and he very quickly fell under its dark influence. Renewed, Helm laid siege to his enemy's fortress, intent on retrieving his daughter from the warlord who had taken her.

Confronting his enemy in his chamber, Helm's daughter Bernwyn asked Siric not to fight her father, before the warlord threatened Hammerhand, claiming that killing him would start a war, to which Hammerhand declared that war had come, before attacking his enemy with his great warhammer.

However, in an attempt to stop her father, his own daughter Bernwyn stepped forward in front of his hammer, causing him to accidentally knock her down and kill her. Enraged, Helm proceeded to take his hammer and kill both friend and foe in the chamber where his daughter died, even going so far as to kill one of his own men with his helmet.

At some point after this event, Hammerhand fell completely into darkness and became a Ringwraith under the slavery of Sauron, enslaved to the will of his Dark Lord and the One Ring.