His name was Yahweh, also called Elohim.
Judaism evolved from earlier religion, which evolved from earlier religion until it was all just tribes believing in their ancestor spirits and whatnot. Religious ideas have to be created and spread and remixed and remastered. The conception of God could not have been done any other way.
The Wikipedia page on Yahweh states that while the origins of the name Yahweh are unknown, the Isrealites were originally Canaanite, and the Canaanites had their own pantheon of gods with names familiar to people who play lots of RPGs, names like El, Asherah, and Baal. El is obviously the root of Elohim, and was the head of the Canaanite pantheon.
It’s thought that the name Yahweh was brought over by traders from a Levantine tribe called the Kenites. This hypothesis solves a number of Biblical conundrums.
Over the course of a few hundred years, history shook out so that the believers in Yahweh triumphed over the peoples that believed in Baal, the legacy of which you see today in the fact that all those RPGs you play have Baal as a personification of evil.
Historical methods have allowed us to move past having the only legible source of truth for that point of time being the Bible, but the period in which Yahweh beat out Baal is chronicled in the Books of Judges.
The book brilliantly weaves a tale of how Israel came to need a singular monarchical state to save them from constant warfare. We today think about Gods in the Christian sense, as these kinds of non-physical entities that people believe in, but the Hebrew conception was slightly different.
Rather than gods and demigods like the Greeks and Norse pantheons, the Hebrews attached divine significance to tribes and the leaders of those tribes. The idea is that the storyteller can enchant with a fantastic tale and then articulate the true history behind it. He can tell the tale of David and Goliath, which would have been loosely based on real history. Anyone who knew the real history could then add on details, and a pleasant evening could be had for all. They didn’t have Netflix, you know.
Naturally no historical analysis was possible so the tales and history slowly blended together over time. Hundreds of years later scholars would write the stories down, and then other scholars would analyze them and make decisions about what to canonize, or put into an anthology.
The rules of storytelling are such that it makes little sense to even attempt to be 100% faithful to old tales, but to just reinterpret them to fit modern expectations. It just didn’t matter anymore.
This fashion of cultural and religious syncretism survived until the Isrealites met the Romans. The Romans did so much damage to the fabric of Jewish (the name for the people changed over time from Canaanite to Isrealite / Hebrew to Jewish) society that people wanted a new way to think about themselves and their religion.
Their usual answer to divine calamity, of which obviously Roman conquest was an example of, was to make a new covenant with God. This time though, the covenant was also with the Romans, who spread the new Christian religion far and wide.
Messianic Judaism managed to survive and evolve to this day. Religions never stay static, they’re always moving.