Most likely the first human who invented the first god was some smart tribal guy who saw that it was a very effective way to protect himself from bodily harm by the stronger ones if he made them and the less smart members of his tribe believe he had a very strong friend living across the mountains…

Source: http://churchandstate.org.uk/2016/04/religion-oldest-weapon-of-mass-destruction-in-human-history/?fbclid=IwAR16du8k-vgVFOc9GC74uYeU2z_8phjxJK5Ehu_wjmCMRqGgkMDDB4oJj6g