YHVH (more commonly written as YHWH or Yahweh) is considered to be the true name of the god of the Hebrews and the religions that were birthed from their traditions, including Christianity. It is often referred to by the Greek term Tetragrammaton, meaning "four-letter word." The same as with his less-specific name, " God," YHVH is credited in Abrahamic tradition with creating the world in six days, establishing the nation of Israel, and sacrificing his son as a messianic figure.
Pronouncing the name was considered taboo by adherents, and the act of speaking it was said to have been reserved for specific rituals by the head priest of the Temple of Jerusalem within the Holy of Holies, so that its pronunciation would not be forgotten. Many other terms were used instead to refer to YHVH, such as Adonai (Lord), Elohim (God), El Shaddai (God Almighty), and Sabaoth (Lord of Hosts). Today, Orthodox Jews will argue that "Yahweh" is not the correct pronunciation of the Tetragrammaton, saying that it is unknowable and unpronounceable, and will spell God's name as "G-d" so as not to profane it.
The spelling "YHVH" as opposed to "YHWH" is a result of Jewish scholars in Germany compensating for the fact that the letter "W" in German has a hard "V" sound, replacing it with the letter "V," which has a soft "F" sound in German, to better emulate the original pronunciation.
Appearances in Megami Tensei
YHVH appears as the final boss in both Megami Tensei II (and its Kyuuyaku Megami Tensei remake) and Shin Megami Tensei II. He also directly affects the plot of, though does not actually appear in, the first Shin Megami Tensei, where he orders Thor to unleash a rain of nuclear weapons on Japan in order to stop the demonic outbreak in Tokyo.
His physical presence is portrayed as a large, disembodied blue or yellow bald head. This design would later go on to influence the design of the final boss of Shin Megami Tensei: Nocturne, Kagutsuchi, and the various different alignment bosses in Devil Survivor and Devil Survivor: Overclocked.
Megami Tensei II
In the post-nuclear world of Megami Tensei II, YHVH serves as the game's final boss after the player defeats Satan. He is level 150, significantly higher than most other demons in the game. His battle also has its own musical theme, called "Omega"; it is a more intense variation of the same theme that played for the battle with Satan, and would also appear later in Majin Tensei.
Shin Megami Tensei II
YHVH first appears in Shin Megami Tensei II as a false image created by believers in The Center, where privileged humans live within Tokyo Millennium, the game's setting. This false image will appear after Aleph defeats the three angels posing as elders within the Messian church, Uriel, Raphael, and Michael. After the defeat of the false image, YHVH threatens to punish Aleph and his generations for all time.
Later in the game, a defeated Lucifer will tell how he was an agent in YHVH's plot to eradicate humanity by summoning Kuzuryu, the great dragon of the mountains of hell, after using Moloch's tail drill to gather enough magnetite to do so. After Kuzuryu's defeat, Aleph enters Eden back on the surface world, which in actuality is a project to shuttle worthy humans off Earth and onto a new planet. Depending on the player's alignment, Aleph's final battle with YHVH can vary.
If the player is Neutral or Chaotic, Aleph must also face off against the personified names of YHVH, including Elohim, Shaddai, and Sabaoth before eventually challenging Satan and YHVH himself. Even if the player is Law-aligned, after YHVH's praise of Aleph for doing his will, Satan will betray YHVH, resulting in the final showdown.
Because of this deicide, as mentioned in a supplementary cutscene, it is theorized that Shin Megami Tensei: Nocturne's Jyoji Hijiri is actually a damned Aleph, forced to live life after life and death after death in a cycle of eternal return where he ultimately cannot affect the outcome of any new creation.
Portrayal in Megami Tensei
The merciless, genocidal demeanor given to YHVH in the Megami Tensei series is often cited as one of its more controversial aspects, especially when coupled with his role as final adversary for each game in which he appears.
However, the true source of this interpretation stems from certain events in the Torah and elsewhere in the Old Testament where YHVH acts wrathfully towards his own Israelites, their enemies, and whole populations of humans that do not heed his word and law--directly influencing the plot elements of causing nuclear destruction to Japan in the first Shin Megami Tensei and wiping out humanity by way of Kuzuryu in Shin Megami Tensei II.
The most famous example of YHVH's wrath in the Bible is the Great Flood, in which he ordered the one godly man on Earth, Noah, to build an ark for his family and all animals, to survive the worldwide destruction.
The Flood is enacted by YHVH because, according to Genesis 6,
The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. So the Lord said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them." --Genesis 6:5-7
Other examples include the destruction of the twin cities Sodom and Gomorrah, the testing of Job in conjunction with Satan, the intentionally false prophecy of Micaiah that lead to the death of King Ahab of Israel in 1 Kings, and an "evil spirit of the Lord" possessing King Saul in 1 Samuel 16.
Series creative director and artist Kazuma Kaneko also responded to a question asking about the nature of YHVH's character, saying,
"...there are many mysterious common motifs, like the flood legend in mythology...One way of thinking is that there was one mythology in the ancient past, and then the races moved...However, the basis is the same, even though there are differences in the myths..And when I thought about what mythology served as a basis, I concluded that it was the Old Testament. Which means YHWH, the god the Old Testament, is the basis for all of the gods around the world, from a folklorist's standpoint."
The question of YHVH's true nature was historically first asked and addressed by the Gnostic Christians who flourished in the 2nd to 5th centuries AD. Because they saw the god of the Old Testament as wrathful and violent, in contradiction to the peaceful message proposed by Jesus, their resolution was to create the demiurge, Yaldabaoth, a corrupted being who created the material world and acted as a false god within the Old Testament. One of the tenets of Gnosticism was to reach beyond the tainted material world of Yaldabaoth and achieve gnosis, or knowledge, of the nature of the one true God who was endless light, who was identified as the same who was the father of Jesus.