they are part of a made up mythology with the aims of controlling human thought as all religions have done since their invention.
humans existed for thousands (thousands...a looooooong time yes?) as hunter gatherers , much as aboriginies and tribes in the amazon do today without these myths and savior religions.
organized religion and these specific archtypes didnt arise until civilization got so bad that the idea of being "saved" caught on like wildfire.
civilization is an inherently flawed way to live, based off materialism and hierarchy and a worker class. religion is one of the many mutated versions of of inherent spirituality in human beings.
if atlantis, the mayans and rome are any indication civilization is a biologically demented way to live and always fails.
the way were going we'll either wipe ourselves out or end up as controlled biological robots (we practically are now)
so my answer to you is that they are myths given relevance by our thoughts, as relevant as spider man or superman or santa.
-clark
http://superstrangeland.blogspot.com/