A warlike member of the "underground people," the sole survivors of a centuries-old civilization whose scientists fled the upper world in prehistoric times for a new home far beneath the surface of the Earth in order to escape the dire peril of advancing glacial ice. In Kyack's words:
Our race once populated the Earth in abundance. Then came the Ice-Age!... Most of us perished under the irresistible approach of the colossal glaciers. But the most intelligent of us, the scientists, retreated deep into the Earth toward its warm center. We built this retreat, equipped it with all the marvels our scientific ingenuity could fashion.
By November-December 1941, Kyack and his henchmen have kidnapped young Tulan, the peace-loving leader of the underground people, as the first step in an elaborate scheme to destroy the structures of the surface world with a diabolical "ray-apparatus" and then invade the world above with an armada of "bore-vessels" designed to enable the villains to extend their dominion over the entire planet Earth.
The savage scheme is thwarted by Superman, who burrows to the cavern city of the underground people far beneath the earth, demolishes the awesome "ray machine" that has been causing buildings in Metropolis to shatter and crumble, defeats the armada of mighty bore-vessels, and restores the peace-loving Tulan to the leadership of his people (S No. 13/4).