It is likely that you have heard atheists say to Christians, "But who created God?" They ask this usually when the Christian has shown that the universe had a beginning, and so in the atheist's mind it's a little like, "If I can't have an eternal universe, then you can't have an eternal God." But does this question really present a problem for Christianity? In this video, Randall Niles explains the impossibility of infinite regression, showing there must be an uncaused God.
There are arguments that can be given which show that the uncaused cause of the universe must be personal, meaning that it must refer to God and not simply to a singularity. Check out the Kalam Cosmological argument article for more information.
