Gunmar the Black is the warlord of the Gumm-Gumm Army and father of Bular. He has been imprisoned in the Darklands for centuries along with his army of Gumm-Gumms by Deya the Deliverer. He is the true main antagonist of Trollhunters.
Nothing is known about the appearance of Gunmar, but when he is seen through the Killahead Bridge, he appears to have lost his right eye.
Gunmar was born from the first Heartstone of the Troll race. When the wars between Trolls and humans were unleashed by the domination of the surface, the horrible deaths and bloodshed corrupted the Heartstone, causing it to rot from within, and from inside it Gunmar was born. The first of his many victims was the king of the Quagawumps. He fought with several Trollhunters, however, none were able to defeat him even with the Sword of Daylight.
He fought against Orlagk for the right to be the warlord of the Gumm-Gumms, a battle that ended Bronyak's death and the loss of Gunmar's eye. After the Troll realm and the human realm separated, Gunmar led the Gumm-Gumm Army to take the power of the surface and to devour all of mankind. This unleashed a war between the Gumm-Gumms and the rest of the Trolls that ended when the Trollhuner, Deya the Deliverer, defeated Gunmar, exiling him and all his army to the Darklands.
Centuries later, his son Bular teamed up with the Janus Organization to piece together the pieces of the Killahead Bridge under the guise of the Arcadia Museum, headed by the chief curator and fellow changeling Nomura, Otto Scaarbach and Walt Strickler. The changelings and the Gum-Gum managed to open up the Bridge with the amulet that they had retrieved from Jim Lake, and Bular briefly was able to speak to his father before contact was lost. The bridge was eventually destroyed by Draal, who removed the amulet before Gunmar could be freed from the Darklands.Upon learning of the death of his son, Gunmar sent Jim a message through Gnome Chompsky, who had been sent into the Darklands through a Fetch some time prior, threatening to murder everyone Jim had ever loved for killing Bular. In the threat, translated by Blinky from Gnome Chompsky, Gunmar promised an 'ocean of blood' for Jim and his loved ones, that he would 'make a throne from their bones'.