In the fictional world of Glorantha, it is thought that the first thing that evolved from Primal Chaos was Darkness, and all other things evolved within the Darkness to form the world. Thus, the Darkness gods are the most primal, and in many ways the most powerful, deities of Glorantha.
Darkness and cold are represented by the Darkness Rune. In combination with the Man Rune, it signifies Trolls ("dark man"). Trolls are the native mortals of Hell and the Underworld, and it comes naturally to them to worship the deities of Darkness. When Orlanth slew Yelm, the Sun, the trolls were driven forth from Hell by his hateful light. They conquered the lightless surface world, and fiercely defended their new domain from the ravages of Chaos. In that war, their mother-goddess Kyger Litor was cursed by Chaos so that trolls would breed degenerate trollkin. Thus, trolls have an antipathy toward Light cultists, and hate Chaos passionately.