The semitic monotheistic god originally was EL. Seen as the old father in the Ugarit pantheon being replaced by Baal. Studies I have read say that the Semitic God was originally monotheistic but then was incorporated as the head of a family pantheon later in Canaanite religion. El also appears as Elohim in the Bible. Baal is seen as the ultimate demon in the bible, the representative of paganism. There were images of El in Ugaritic worship which have survived.
So we know that both Mesopotamia and Egypt were first polytheistic. Later in Egypt there developed the idea of the trinity Ra, Aten (related to atom and Atum), and Amun being the three faces of this ultimate God. This is more ore less like Hinduism that recognizes Brahman as beyond the trinity of Shiva, Brahma and Visnu. This is more or less on the same template as Ahura Mazda and Angra Mainyu (Ahriman) where Zurvan is the abstract parent of the two warring brothers. Zurvan is an artificial after the fact abstract construct to unite the dualism of the waring twin gods. Vishnu was a Nondual manifestation of the God Head as a person to unite the gods of the north Brahma and south Shiva. So these are two examples of late syntheses.
In the case of Ra, Aten and Amun we have a more sophisticated concept. Aten is the sun disk. Ra is manifestation, i.e. everything that can be seen in the world by the light of the Sun, i.e. the sun as active manifestor of the things of the world. Amun is the hidden god. My idea is that like Akhnaten took Aten as the only god, so Moses took Amun as the only god. He took the name Yhwh from the local name of God at the mountain where he encountered the vision of gods burning bush and his hearing of Gods words directly. But this was a hearkening back to the God EL who Abraham had encountered on leaving the polytheistic society of his birth in UR, the origin of Mesopotamian society.
It seems that the Semits always worshiped an original montothestic god in the deserts between Egypt and Mesopotamia, which Muslims now call Allah. Allah is considered a unique name and not “The God”, i.e., Al-ilah. There is no god “Lah” (subsequently the questioner changed his question to reflect ilah instead of Lah) historically. This is a misunderstanding. However, Allah (formal name) is The God, i.e. the only god in Muslim eyes. And it appears that this is the original El worshiped as a monotheistic god prior to pantheism. Thus it is interesting that there was an original monotheism between the two pantheisms of Mesopotamia and Egypt. Gods in Mesopotamia the orignal titans have the prefix EN, like Enki and Enlil etc. On the other hand the gods of Egypt were originally polytheistic too being all local gods that were by synchronism combined into myriad trinities the highest of which was Amun, Aten, and Ra. Greek gods are on the Uagritic/Semitic pattern rather than the egyptian pattern. The titans are the original Mesopotamian gods.The innovation of the Greeks was to give their gods human form without animal (totemic) representations, so that the gods were perfect mirrors of humans. The Olympians are there immortal archetypal mirrors of mortals that are human all to human. Totemic Egyptian Gods were distant from humans and kept within temple sanctuaries, dressed and fed by their priests. Greek Gods roamed the world freely.
Indo-Europeans the other group that influenced the Greeks had gods related to Caste as Dumezil has shown.
Greeks took the Mesopotamian Gods as the Titans, and then took the Ugritic family structure as the pattern for the Olympians. Their only concession for to the Egyptians was in having Zeus and Hera brother and sister marry in order to show that they were like the Pharaohs who were gods on earth. Totemic aspects only come in by the transformations of people and gods, and lower entities like Saytrs or Centaurs etc. But the syncretic nature of the Greek gods is that they take something from each of the precursor traditions, but then add in the isomorphy between mortals and immortals.
Thus we can see if we look closely that there are several different patterns for Gods that were on a collision course and came together in the emergent appearance of the Greek Gods which as a true innovation. All polytheism is not the same. And Polytheists do not lack a concept of The God who is behind all the manifestations of the various deities they worship, just like Aristotle and Plato talk about God beyond all the plethora of immortals in myth. The indo-European traditions has caste based gods and the idea of their deva/assura split. In the Vedas the Assuras were the elder gods and the devas were the newer gods like Indra, Vayu, etc. The Titans in the Vedic tradition are gods like Mitra and Varuna. When this pattern was brought to the Mediterranean then we could take the elder Mesopotamian gods as the Titans and take the Ugritic gods as the Olympians. Zeus is Baal. From the Hittites we get the succession myth going from Ahlu, to Uranus, to Cronos, to Zeus/Hades/Poseidon (A trinity). Of these only Poseidon is an orignal Indo-European god. Totemic spirits like the Egyptian Gods are always lesser demigods or peripheral monstrous creatures to be fought by the mortal-like immortals of Greek Myth. In Greek myth we get a perfect mirroring between the human and the transcendent gods as an emergent event, seen in their human like representations of their gods. On pottery we only know we are looking at gods because of their labels and because of their iconography of their accouterments. Ironically the more the Gods became to resemble the humans the more alien they became because they represented true transcendences of mortality in human form.
In other words totemic gods are easier for humans to relate to, as for instance they relate to animals who are other creatures on a different plane than themselves. So if we take Human and Animal characteristics and combine them to project a transcendental plane above the human, then we can relate to that plane as we do to animals. We are the animals in relation to that higher level plane of existence. So Totems are to us as we are to animals, and they take partially or wholly animal form but deified, so we get caves full of mummified cats. The mummification is the sign of the God like properties of the totem. The animal is transformed though the human to the hither plane to be worshiped. And the god is kept in an inner precinct and clothed and fed by the priests, and occasionally paraded though the city. This practice was taken up by the Greeks who build temples based on Egyptian stonework, which was then perfected by the Greeks. But the Greeks had representations that were human like sculptures as their idols rather than resorting to totemic masks as would the Egyptian priests who enacted the role of the gods in rituals. Rather the Gods were considered as invisible, but they could be projected into human form. So rather than the humans taking on the appearance of the Gods via the totems, the gods took on the appearance of humans, or sometimes animals. So the Gods transcended down, rather than being projected as the inverse of the animal plane of existence.
But from the Egyptians the Greeks also inherited the idea that beyond the gods was the Godhead. Interestingly before we could read the Hieroglyphs the Europeans scholars figured out that this must be the case and hypothesized that this Godhead beyond the Amun/Aten/Ra trinity was the source of monotheism. But rather scholars that have studied the Ugaritic materials believe that there was an original monotheism among the semites in the desert between Egypt and Sumeria, which then become degraded into a polytheism with El becoming the chairman of the board of the Ugaritic pantheon due to polytheistic influence from the surrounding cultures, especially Mesopotamia.
So from this we can see that there are different types of monotheism. There is original archaic monotheism that Islam is attempting to reinstate. Then there is also the abstraction of Polytheism, which is conceptual that posits an idealized synthesis like Zurvan beyond the multiplicity. Next there is the conceptualization of a Godhead as we can see lying behind the trinity of Shiva.Varuna.Brahma, i.e brahman, or explicitly included in the trinity in the form of Amun, which is beyond Aten and Ra as an invisible transcendental.
We see Moses, who was one of the Jews who were in Egypt at the time when the Palestinians ruled Egypt. He took the idea of Akhnaten and took Amun instead of Aten as his God, but he named it Yhwh after then name of the original monotheistic god of the Semites that came from the desert area where he had his encounter with El, the oriental monotheistic god, who properly is The God, or Allah.
Christianity unfortunately fell back into Trinitarianism with the idea of the Avatar of the Father God. Here the relation between God and man is mediated by the Angel (Holy Spirit), and eventually it became dogma that This man Jesus become Christ on his resurrection. This idea had nothing to do with the teachings of Jesus himself, which are preserved in the pre-Q Gospel of Thomas which is aligned with the view of Jesus in Quran which is considered gnostic by scholars.
Gnosticism is really influenced by Manicheaism a late heresy of Zoroastrianism that combined Buddha, Zoroaster and Jesus as procurers to Mani whose revelations are more wild than any science fiction today. Mani was given to reinterpreting previous religions in wild and wonderful ways a tradition carried on by the Gnostics. Since the Gospel of Thomas was pre-Q it becomes the closet thing we have to the actual words of Jesus, and there are no claims to be God in these as we see first in the Gospel of John.
In a way we can see christianity as the degeneration of the greek mirroring between mortals and immortals by the introduction of Avatars, and Spirits as being identical yet different in the iron triangle of the trinity. In other words making them identical destroys the mirroring. The Paulistic synthesis of Mithrism and Messanic Judiasm while ignoring the actual teachers of the founder of the religion is a very unlikely candidate for a world religion. But when we understand the nature of slavery in the roman empire and the denial of the body by Greeco-Roman philosophies, we can see Christianity as a structural inversion that celebrated the body, and embodiment. If God can have a body then it must be OK, in spite of the suffering, because God suffered too, and in fact lifted our burden by suffering for everyone thus redeeming our sins, etc. The mirroring between mortals and immortals is replaced by a mediated identity within the trinity, which is just another variation on the trinities we have already seen in action in Hinduism and Egypt, not to mention in Greece. Of all these the most sophisticated trinity is the Egyptian one, because it has Amun the invisible nature of God juxtaposed to its concrete body Aten as sun disk and Ra as manifestation of the world via light. Moses used this sophisticated idea of the invisible god to return to the semitic archaic monotheistic roots calling it Yhwh, which later Muslims called Allah. El=Yhwh=Allah. Islam rejects the trinity of Christianity that makes a man, as avatar, God. It also rejects the bible as original revelation.
All this is a complex way to say what you mean is El not Lah. Lah is just a mistake. (subsequently the questioner changed his question to reflect ilah instead of Lah) There is no Lah as Al-Lah behind Allah. There is instead El or Elohim, who become Yhwh which much later was called Allah. The point is that these are attempts to unearth original monotheism as opposed to synthesized unities like Zurvan or Brahman. Original Archaic unity of monotheism is not an idea like Zurvan which tries to rise above diversity. Rather original unity is non-conceptual and nondual. None of the structural transformations of differentiation and articulation of multiple gods, or even an imposed idea of GOD later like in Egypt, or Greece, or Hinduism, can capture the original archaic monotheism. As soon as you say One or Many it is lost. The oneness of archaic monotheism comes from the amorphousness of differentiation not having yet arisen. No thought of two or many has arisen, so we don’t have to reimpose the idea of oneness as unity and totality in order to reclaim in the abstract what was lost in the archetypal oneness of the undifferentiated God worshiped when there was only one possible God.