The Evil-god challenge attempts to undermine classical monotheism by contending that because belief in an omnipotent, omniscient, omni-malevolent God (the Evil-god hypothesis) is similarly reasonable to belief in an omnipotent, omniscient, omnibenevolent God (the Good-god hypothesis), the onus is on the classical monotheist to justify their belief in the latter hypothesis over the former hypothesis. This thesis explores the Evil-god challenge by detailing the history and recent developments of the challenge; distinguishing between different types of Evil-god challenge; responding to several (...) prominent objections to the challenge; and applying the challenge to philosophical arguments for the existence of God. I also evaluate the efficacy of parallel arguments as a whole, with a view to determining the parameters of the Evil-god challenge by laying out exactly which theistic positions are irrevocably undermined by it. I conclude that the Evil-god challenge effectively damages several arguments for the existence of God and, in cases where it does not straightforwardly do so, it nevertheless reduces the Good-god theist’s belief to one or more intuitions. (shrink)