I've read that Yahweh used to be the god of war or thunder (depending on the source) in a polytheistic religion worshipped by ancient Canaanites, but none of my sources backed up their claims with evidence, and this seems very interesting and something I'd like to learn more about.
And it seems that information like this, if true, would be more widely known and used as an argument against the Jewish religions (and the religions that branched off from that such as Christianity and Islam). I actively seek out arguments like this online, but have only seen it used as arguments against the Jewish monotheism a single time without explicitly searching for it.
For more information you might check out the thread at /r/AcademicBiblical on the shift from polytheism to monaltry.
When did the Hebrews transition from polytheism to henotheism, to monotheism?
Do you mean El Shaddai, the 'God of the Mountain?'
Follow-up: was the transition to strict monotheism or to monolatrism? That claim was made in Snow Crash, and I've wondered if there's any truth to it.