Bible believers often claim that the god-name YHWH or Yahweh means "He Who Is". As someone has just argued it once more on a forum in which I participate, please allow me to state my view on the matter. The claim is a mistake.
As Julius Wellhausen first theorized, YHWH is from the Arabic root HYW, "to blow/storm". It is an ordinary Arabic root, attested in the Quran. The form Yahweh would amount to "He blows", a normal format for names and particularly god names in ancient Semitic. The root is not attested in the closely related Hebrew language, and this narrows the origin of the name down to an Arabic or at any rate non-Hebrew setting.
This tallies neatly with the Biblical account of Yahweh's first appearance. Indeed, the book of Exodus relates that Moses, who till then had always lived in the Nile valley with its stable ever-sunny climate, finds the new deity YHWH while staying with the Midianite Beduins, who live in the desert with its unpredictable sand storms. Remember that Moses had been found out after murdering an Egyptian, then fled and took refuge among the desert dwellers, whose priest was called Jethro. He stayed there for quite some time, even marrying Jethro's daughter. (That Midian resembles Medina, the name of Mohammed's headquarter city, and Jethro resembles that town's original name Yathrib, is considered by some to tally nicely with Kamal Salibi's theory that the Biblical scenes were not set in Palestine but in Arabia; but we'll put it down to a cute coincidence.) It is in the desert that Moses finds Yahweh, addressing him through the Burning Bush, a typical desert phenomenon of ethereal oil from a plant catching fire under the immense heat from the midday sun.
YHWH is thus a typical weather-god, comparable to Indra, god of the thunderstorms breaking the monsoon rain. That may well be why He is deemed to control atmospheric phenomena, including the natural causes of some of the Ten Plagues of Egypt as well as the Parting of the Sea.
When YHWH appears in the Burning Bush and replies to Moses: "I am what I am" (Ehyeh asher ehyeh, Exodus 3:14), it seems to be an affirmation of total sovereignty, meaning that he is under no obligation to inform Moses about Himself. This is confirmed by parallel sentences like: "I do what I do", clearly intending the speaker's absolute sovereignty and independence. The word asher is a relative pronoun, meaning "(he) who" or "(that) which)". But it has often been rendered wrongly as a subordinative conjunction, "that" as in "I can see that it's raining", so that the Biblical sentence comes to mean: "I am that I am", e.g. in the King James version. In contrast with the perfectly normal sentence, "I am what I am", you get a bizarre sentence that nobody ever utters, "I am that I am". Its intended meaning, thus explicitated by numerous interpreters from Antiquity till the present, is something like: "I am the One Who Is", "I am the One Whose Being or Existence is necessarily the case".
Given this theological reading, it comes in handy if the name YHWH itself could be analyzed in a similar or related sense. And so, the four-letter word has come to be explained (no doubt in good faith, for the Bible editors were not schooled in etymology) as an unusual and contrived form of the Hebrew verb HYY, "to be", viz. "He is". That would also make it into a proof of God from etymology: God must exist, for His sacred Name says so.
Seductive and imaginative as this explanation may be, it must nonetheless be dismissed as a typical example of folk etymology. There is nothing particularly shameful about this: before the birth of modern comparative-historical linguistics, the only etymology available (e.g. in Plato's Cratylus) was of this fanciful prescientific kind. But repeating such explanations today, when linguistics offers a more accurate though less heady explanation, would have be considered as sophomoric cleverness.
Julius Wellhausen (1844-1918) abandoned his professorship in Theology when he realized that his uncompromisingly secularist reading of the Bible was incompatible with the job of preparing students for a career as Christian ministers. He shifted to Oriental Philology in order to have the freedom to go where his scholarly insights into scripture took him. His great legacy is a candid demythologizing approach to the Bible as a piece of human literature rather than the Word of God. Among other things, his contribution was decisive in establishing the distinction between four editorial traditions that together constitute the Biblical text.
Though he was opposed mostly by traditional Christians, later detractors have tried to overrule the German professor's findings with the imputation of anti-Jewish motives. I have not seen any evidence for that all too predictable allegation. It would in any case make no difference: the truth of a scholarly hypothesis is not dependent on the motives of its proponents. Sometimes people say the truth for the wrong reasons, just as untruths are sometimes believed and propagated by people with the nicest of motives. So, I salute Wellhausen as a pioneering Orientalist, an explorer and map-maker of religion as a human construct rather than a divine revelation.