The origins of Yahweh

The judeo-christian God, as much as it's modern worshippers protest, has clear mythological origins in the beliefs of the Ancient Middle East. For a long time, associations with the Egyptian Aten and the canaanite El (the latter of which assimilated by the cults as an epiphet), but more recent historical finds seem to suggest an unique position in the semetic pantheon.

Yahu is a common name in canaanite inscriptions. It reffers to a war deity, son of the dominant god El and his consort Asherah, that was seen as the patron of armies. Variations include Yahwi, Yammu, Yaw and Yahweh, the latter gaining popularity in latter periods.

The first depictions of Yahu come from Egypt, suggesting that it had an african origin. However, it was a fairly minor deity until the 14th century BC, where it was worshipped in southern Canaan, becoming the local dominant deity. Early semetic peoples were henotheistic, whence why Yahweh/Yahu quickly became the primary god worshipped by them. Even as recently as the writing of the Old Testament, however, Yahweh/Yahu's cult did not exclude worship of other deities secondarily, hence modern judeo-christian monotheism is fairly recent.

Predictably, as Yahu's worshippers expanded, he was combined with the dominant gods of the canaanite pantheon, especially El and Shamayim.

As a final note "Yahweh" does not mean "I am". If anything, it was the other way around; as Yahweh rose in predominance, it's status as a dominant god created a change in its meaning.

Refs:

Archaeology of the Hebrew Bible, R. Giveon (1964), Theological Dictionary of the Old Testament.