Albert Einstein was one of the most intelligent people to ever exist on this planet and he described himself as an agnostic. Here are his own words on the subject of God, atheism, and agnosticism:
I have repeatedly said that in my opinion the idea of a personal God is a childlike one. You may call me an agnostic, but I do not share the crusading spirit of the professional atheist whose fervor is mostly due to a painful act of liberation from the fetters of religious indoctrination received in youth. I prefer an attitude of humility corresponding to the weakness of our intellectual understanding of nature and our own being.