Who is Kevin from Valis and what is their importance?

A friend of Horselover Fat's, Kevin (surname never given) is a thorough-going skeptic. He and his ideological opposite, the staunchly Roman Catholic David (also no surname given) are, with Philip K. David and Fat, charter members of the Rhipidon Society. Kevin obsesses about why God allows his pet cat to run under the wheels of a car. He sees this demonstrating that God is evil, dumb, and weak, and Kevin intends to demand an answer at the Last Judgment. Kevin's cynicism only intensifies Fat's madness.