This is the one cross-cultural comparison on this site where the strong version of the claim survives scrutiny — and only for part of the list. Six thunder gods are usually named together. Four of them belong to a single language family and can be linked by reconstructed vocabulary and inherited poetic formulae. The other two cannot, and the difference is not a technicality.
The reconstruction that holds
Comparative linguistics reconstructs a Proto-Indo-European weather god whose name is written *Perkʷunos. The reflexes are unusually clean: Lithuanian Perkūnas, Slavic Perun, and — with the phonology working out exactly as the rules predict — a Germanic form surviving in Old Norse as Fjǫrgynn, a name attached in the sources to the parent of Frigg, and in the feminine Fjǫrgyn as a name for Thor's mother, the earth. Vedic Parjanya, a rain god, is usually included though the derivation is debated.
Alongside the name sits something rarer: an inherited phrase. Calvert Watkins showed that the collocation "hero smites serpent" survives with cognate verbs across Indo-European poetic traditions, and the thunder gods are its principal subjects — Indra striking Vritra to release the waters, Thor against Jörmungandr, Zeus against Typhon. When two languages share not just an idea but the specific verb used to express it, borrowing and coincidence become poor explanations.
Add a third inherited element — the weapon that returns, or that is a stone rather than a blade. Mjölnir comes back to the hand; Indra's vajra is a thunderbolt fashioned from a sage's bones; the Baltic god's weapon is a stone axe, and prehistoric stone axes turned up in fields were called thunderstones across northern Europe well into the modern period. Miniature hammer amulets from Viking-age graves are the archaeological end of the same idea.
That is a real result, and it should be stated as such rather than diluted into "many cultures have thunder gods".
Now the part that does not transfer
Adad is Semitic. His name belongs with West Semitic Hadad, the storm god later worshipped as Baal in the Levant, and there is no reconstructable relationship to the Indo-European set. His profile is also different in an important way: in a land farmed by irrigation rather than rain, storms are more threat than blessing, and Adad appears in omen literature and treaty curses as an agent of destruction — flood, hail, ruined harvest — at least as often as a bringer of fertility.
Raijin is further away still. The familiar drum-ringed demon-faced figure is fixed by early seventeenth-century Japanese painting, and the connection between that image and the eight thunder deities that emerge from a corpse in the earliest chronicle is a matter of convention rather than continuous textual descent. Nothing links him to *Perkʷunos except the weather.
Taranis is a special case worth handling carefully. His name is transparently built on a Celtic root for thunder, which does place him in the Indo-European family — but almost everything else said about him comes from a single Roman poet's list of gods to whom the Gauls made human sacrifice, plus a scatter of inscriptions and a wheel symbol found on Gaulish material. He is a genuine cognate with almost no attested mythology, and the elaborate Taranis of modern books is largely reconstruction.
Four different jobs
Once you stop asking who throws lightning and start asking what the god is for, the six separate cleanly:
- Thunder as sovereignty. Zeus rules, and the bolt is the instrument of a king's judgement rather than a warrior's weapon. The rest of his profile — oaths, suppliants, assemblies — is legal. The contrast with the Norse arrangement, where the thunder god is not the king, is examined at Zeus and Odin.
- Thunder as protection. Thor defends the boundary of the inhabited world against the powers outside it, and his popularity among ordinary people appears to have exceeded that of the god who outranked him. His fights are with giants and monsters, not with rivals for a throne.
- Thunder as fertility and release. Indra's central act in the Rigveda frees the imprisoned waters, which is a rain myth and an agricultural one; roughly a quarter of that collection concerns him. His later decline into a humiliated middle-ranking deity in the Puranic material is one of the most dramatic status reversals in any pantheon.
- Thunder as portent and menace. Adad in omen texts, Taranis receiving what a hostile Roman source describes as human sacrifice, and Raijin as a figure to be warded off — including the folk instruction to hide your navel during a storm. Where storms are unpredictable rather than seasonal, the god is a danger to be managed.
The comparative frames, and how much weight they bear
Georges Dumézil's trifunctional model assigns the thunder god to the second function, that of force, distinct from the sovereign function above and the productive function below. It works elegantly for the Norse arrangement and less well for the Greek, where the sovereign holds the thunderbolt himself. Dumézil's system remains genuinely productive and genuinely disputed — the standard criticism is that a large enough pantheon can be sorted into any three categories if the sorter chooses which gods are central.
Nineteenth-century solar mythology, associated with Max Müller, tried to reduce most Indo-European myth to weather and celestial phenomena and collapsed under Andrew Lang's attacks, partly because the method could turn anything into a sunrise. Its residue is still visible in popular writing that reflexively explains every mythic conflict as a storm. And Joseph Campbell's monomyth has nothing useful to say here at all, since thunder gods are not on journeys.
The lesson is that this comparison is strong for a specific reason — documented linguistic descent — and that reason is unavailable for the pairs that lack it. A genuinely good comparison names its evidence.
Where to read further in this collection
Individual entries carry the detail: Thor and Mjölnir, Zeus and his Roman counterpart Jupiter — whose Optimus Maximus cult on the Capitol is the actual Roman thunder-religion — Indra, Adad, Raijin, and the Irish Dagda whose club and cauldron are sometimes pressed into this frame with less justification than their advocates admit. The serpent-combat thread continues at dragons and serpents.
Questions this comparison usually attracts
Is Thor's hammer really a thunderbolt? The name has been connected to words for crushing and to Slavic and Baltic terms for stone or rock, which fits the thunderstone tradition well. What is distinctive about Mjölnir is not that it strikes but that it is also a consecrating instrument — used to hallow a bride, to bless, and in one story to restore eaten goats to life. No other thunder-weapon in this group does sacramental work.
Why is Jupiter not on the main list? Because he is Zeus's cognate rather than a separate data point: the same reconstructed sky-father name in a different language. Including both would double-count the evidence. Where the two diverge is in cult, not in descent — Roman practice made him the guarantor of state oaths and treaties in a formalised way Greek religion never quite matched.
Does every farming culture have a thunder god? No. Egypt, dependent on the inundation rather than rain, produced no major thunder deity; its storm-associated figure is Set, whose portfolio is disorder and the desert. That absence is a useful control case against the assumption that agriculture generates a storm god automatically.
What about Perun and Perkūnas — are they the same god? They are separate gods in separate traditions descending from the same reconstructed original, which is exactly the relationship Latin and Spanish have. Baltic and Slavic material is also recorded very late and heavily mediated by Christian chroniclers and by nineteenth-century national revivals, so specific claims about their rituals need the same source-scepticism applied to Celtic material.