Zoroaster

Professor Michael Costa wrote in his book about the golden section,Solomon’s seal and the Star of David [Poalim,1990 page 154] that the origin of the Magen David was in the Persian religion of Zoroaster in which the triangle with the edge turning upwards symbolizes the good God Ahur Mazda whereas the triangle with the edge turning downwards symbolizes the evil God Ahriman. In the Zoroastrian hexagram the first is on top o the second in order to symbolize the victory of the good over the evil.
It is interesting that Zoroaster and King David lived approximately in the same generation and possibly one of them influenced the other.