According to modern prophets, Adam taught the gospel to his children. Most rejected it entirely. I don't know whether they believed in some other form of religion before.

All true religion is revealed from God. Imagination only creates imaginary Gods.

Satan will also sometimes appear to man pretending to be God. He tries to lead people away from righteousness.

You probably wanted a more scientific answer based on books and pottery dug up from archelogical sites. The trouble with scientific answers, is that they change from year to year. I remember seeing a picture of the canals of Mars in my science book in grade school. I also remember studying about Cromagnums and how they evolved into Homo Sapiens. Now science teaches that the canals were scratches on a telescope and that Cromagnums are Homo Sapiens.