Who started the other religions?

Theoreticlly,If God created the world...started with two humans and the humans had children...cain, abel...and they had children.lalala...and then after a significant amount of people were on the earth, God destroys the earth and starts out with abraham and his family....they all knew God, worshipped him, all that great stuff....so who went out and started these other religions?what would they have to start them? i mean satan couldnt have just come and told one "oh hey, theres other Gods out there, theres more than just this one" there would have to be proof, if they were knew God and knew about satan and his game plan they would know not to listen to him, they would know he was lying and reject his attempts.