Well I'm not asserting the serpent and Jesus are the same - I'm just saying that was a belief for a time. Beliefs evolve. Remember, the gnostics thought the Old Testament God was evil. But even that is just the outer/exoteric layer. That God was also us. We're Sabaoth, needing redemption. According to them, it was the logos that fell from grace, because it tried to reunify with the Father (the highest God, the source).
I was wrong in saying it was Jesus specifically - Jesus is the name of the man embodied logos, but that body is unimportant. A serpent is a good symbol for logos because logic/story weaves through existence, like a snake. The snake was also already a symbol in Orphism, which was Greek but originated in Egypt (a lot of Greek stuff was actually Egyptian stuff with different names). In Egyptian cosmology, the snake was the eater of worlds. The goal of their spirituality was to not be eaten by the snake - meaning to exit this cyclical world (stop being thrown into the lake of fire (rebirth)) and live eternally in Amenti. Amenti is equivalent to Barbelo, in gnosticism - forethought, aka heaven.
All of this is really just psychology. All the names are the names of stations in your own mind. Its examining the relationship between consciousness and reality. In some text, I forget which, its stated that the aeons sorted themselves according to rank and station - this is talking about the components of your mind.
Switching to Quetzalcoatl - idk much about it, but I do think it's very interesting that they have the same imagery of a man with three snakes rising up on either side if his head, for six total, or seven if you include his head - and exactly the same image can be found in carvings in south Asia - India and east of India. There's obviously some connection.
You could also tie in the Sumerian rulers, who, according to those clay tablets from Ninevah, lived for tens of thousands of years.
I hope it doesn't seem like I believe any of this. I'm partial to the snake/logos connection, but I do keep it compartmentalized from the set of truths and Truth that I've found.