What was Abraham the first to believe in?

Answer 1

Abraham was not the first to believe in the God who would be the God of the Israelites, because Genesis says that he met a priest of this God. Based on this account, there must have already been an entire community that also believed in God.

Abraham was not necessarily the first to believe in one God alone, as The Bible never attributes monotheism to him. A well known Jewish midrash has it that Abraham, while still a young boy, realised that his father's idols had no power, and perceived that there is but one God. But midrashim are no more than rabbinical opinions and can not be relied on as evidence of events said to have occurred almost two thousand years earlier.