He was a powerful Native American sorcerer and the last of a branch of the Mic Mac tribe devoted to the "Night Howler" (in reality Nyarlathotep): despite having apparently died over 70 years prior to the events of the story he was in fact an immortal and hid in the shadows, from there he continued the dark rituals he had performed for centuries and sought to bring about the age of Cthulhu and destroy anyone that got in the way of the Great Old Ones.
Prior to the events of the main story Narackamous mentored Jonas Hambleton in the ways of dark magic and introduced him to the worship of the Great Old Ones - he also helped Jonas in the ritualistic murder of Jonas' own wife in order to appease the sea-demon known as Dagon.
Narackdamous was first encountered when Mr. Parker, an aspiring photographer on the trail of the titular comet of the story, entered the woods and stumbled across the ancient sorcerer and a small cult of Great Old One devotees, calling out the now famous praise of Cthulhu Narackdamous became aware of Parker's presence and flew into a rage.
Narackdamous taunted Parker, saying he had signed his own death warrant that night and pursued him across the forest as if to kill him, while taunting him on the arrival of the Great Old Ones and the apocalypse they would bring -(however he was not nihilistic, he believed he would be spared the evils to come for his service - a trait common to dark magicians).
In the end Narackdamous is pursued to his underground lair by Mr. Parker, after Parker succeeded in slaying Jonas and the other followers - using a bow and arrow Parker pierced Narackdamous' heart and finally ended the dark magician's plans for the apocalypse.
However even with Narackdamous gone Dagon and the Great Old Ones began to manifest into the world, forcing Mr. Parker to spend the last few chapters of the game facing the Great Old Ones themselves in order to avert the enslavement of mankind: climaxing with a confrontation against Yog-Sothoth itself.