What is God?

Religions claim to know the nature of God. But, if God exists, how can humans begin to comprehend the nature of God. So, I put the question out there: What is God, assuming that any sort of God exists at all? I don't presume that God must necessarily exist or not exist. However, I find the notion of a personal God, as depicted in the major religions, extremely problematic, and thus, in my view, very unlikely. I am interested in how others approach this issue.