Albert Einstein rejected organized religion and never stated belief in "God" or gods, but he didn't proclaim to be an atheist either. While he was raised in a secular Jewish household by non-practicing parents, he had spiritual beliefs similar to agnosticism or pantheism.
Though Einstein rejected religion, he also rejected the certainty of atheism. He emphasized humility with respect to the limits of human understanding, a point of view that may seem as ironic considering that he is considered one of the greatest thinkers in human history.
As a child, Einstein may have had religious beliefs, but he lost these with time. In his autobiography, he notes that scientific thinking largely drew him away from religion, with scientific understanding making Biblical stories seem entirely implausible.