At the end of the day- I don't think we can never be certain, even if it feels so- but none the less, we should respect and identify with any possible theories, even those that discount his/her existence, instead of wasting time blowing up innocent people... (you heard me terrorists)
"Whoever was walking down a small street in his town, and met a herb dealer for his local groceries. After purchasing the items whoever walked through the desert to his dwelling, eating one of the herbs he had puchased. A few hours later, whoever began to feel funny- and started seeing funny shapes and colours swirling in front of him, flying gracefully across the desert. Walking through this barren wasteland was initially a task whoever resented, but now whoever felt completely at peace with the desert, and had an unrequited respect for it forevermore- as he swam through heavenly white sand and glimmering golden air the effects simmered away into the breeze, and whoever stood at the edge of the desert lost for words: "guh, uck, heh, god... what the... hell was that..." And so, he wrote the account down on some parchment later that evening. Soon enough, he spread word of his experience, and because he didn't recognise or comprehend the psychoactive nature of the herb whoever purchased, whoever determined that his experience must have been the work of some higher authority- when people observed his story in the local news, they came up with a name for the authority responsible for his experience: the only word that seemed to stand out in the minds of those who read it- God. And hey presto, it became an institution. Soon enough people from all over started experimenting with the herbs he purchased and had mystical experiences of their own: One had an experience fishing one day, and the fish increased in size, until it reached a growth remeniscent of a whale :P and swallowed the person up. Another who studied animals, had an experience in the rain and became convinced it was precipitating for what seemed to be forty days and forty nights- and in desperation, wished for a way to save himself: and at will the trees manifested into a huge ark, with all of the animals studied so far, not to mention creatures yet to be seen, waiting there for him. A third had a bad experience, and saw the sky in blood red torrents, with fire shooting up from the earth... and the list goes on. And eventually, every experience, and other stories inspired by them, where collected into one long storybook- known today, as the bible :P"
'Note: This is only a theory, made for fun- do not attempt to take it seriously, but dont discount it either :P'