He needs less sleep than a bird. He sees a hundred leagues by night as well as by day. He hears wool growing on a sheep's back and grass growing in the ground, and — Snorri adds, as though finishing a list — anything quieter than that too.
Heimdallr is a sensory apparatus with a name, stationed at the end of the sky where the bridge meets the wall, and the horn he is holding will not be blown until it does not matter any more.
The watchman's post
His hall is Himinbjörg, "heaven-mountains," and Grímnismál places it where Bifröst reaches heaven's end; there, the poem says, Heimdall drinks good mead in a pleasant dwelling. That is the whole of his domestic life in the sources. Everything else about him is function.
Gjallarhorn — the yelling horn, the resounding horn — is his instrument. Völuspá says that when the sons of Muspell ride, Heimdall raises it and blows loud, and Odin consults Mím's head. In Gylfaginning the sound carries through all the worlds. Snorri also says the horn is stored under one of Yggdrasil's roots, in Mímir's well, where Odin's eye is, which produces the memorable image of a drinking-vessel and a sensory organ deposited together in the same water — though "horn" in that passage might mean the eye's own vessel, and the identification of Odin's pledge with Heimdall's trumpet is Snorri's, not the poems'.
He is called Gullintanni, gold-toothed, and Hallinskíði, and his horse is Gulltoppr, gold-mane. He is the wolf-avoider's kinsman and Loki's designated opponent: at Ragnarök the two kill each other, closing an enmity that runs through the whole corpus without ever being explained.
Nine mothers
Hyndluljóð says he was born at the world's edge of nine mothers, and names them — Gjálp, Greip, Eistla, Eyrgjafa, Ulfrún, Angeyja, Imðr, Atla and Járnsaxa — sisters, all of them, who gave the growing infant the strength of earth, the ice-cold sea, and a boar's blood.
No source explains the mechanism. The two standard modern proposals are that the nine are the daughters of the sea-god Ægir, so that Heimdall is born of the waves, or that they are giantesses, since several of the listed names belong elsewhere to giantesses — Járnsaxa is Thor's son Magni's mother, and Gjálp and Greip are Geirröðr's daughters. Both are inferences from name-lists, not from any text that says so. The family tree records the nine as given and draws no descent line, because there is nothing to draw one from.
Rígsþula, or how the classes were made
A poem preserved in the Codex Wormianus tells of a god who walks green roads calling himself Rígr. He arrives at three houses in turn and stays three nights at each, sleeping between the couple in the bed.
At the first, a cramped house, Edda and Ái feed him coarse bread and broth. Nine months later Edda bears Þræll — "thrall" — dark-skinned, with rough hands and a bent back, who marries a bow-legged woman with sunburnt arms and fathers a line of labourers with names like Cattle-Bearer and Stout-Leg. At the second house, Amma and Afi give him a good meal; she bears Karl, "freeman," red and ruddy, who breaks oxen, builds barns and fathers smiths and farmers. At the third, a hall, Móðir and Faðir serve wheat bread on a white cloth with pork and roast fowl and wine in silver. Their son Jarl is born fair with piercing eyes, learns to shoot and ride and swim, and Rígr comes back to claim him as a son, teaches him runes and gives him his own name. Jarl's youngest son, Konr ungr — "young Konr," a pun on konungr, king — surpasses even his father in runic knowledge and can quiet the sea and dull sword-blades. The poem breaks off unfinished.
Only the prose introduction identifies Rígr as Heimdall. The verse itself never does. And Völuspá opens by addressing the audience as the "greater and lesser kindred of Heimdall," which is the strongest support for the identification and is still only an allusion. The equation is probably right and it is not certain, and every popular account that states it as fact is skipping that step.
The poem is also a piece of frank aristocratic ideology: it grounds Scandinavian social stratification in divine paternity and gives the ruling class better bones and better manners by descent. Whether it dates from the tenth century or the thirteenth is disputed, and the Irish loan-word rí (king) behind Rígr has been used to argue for composition in the Norse-Irish world.
The fight over the necklace
Húsdrápa, Úlfr Uggason's poem of around 985 describing carved panels in a hall at Hjarðarholt, refers to Heimdall and Loki contending in the form of seals at Singasteinn over the Brísinga men — Freyja's necklace. Snorri quotes the passage and adds nothing useful.
That is all that survives of what must have been a full narrative: two gods as seals, fighting over a piece of jewellery on a rock in the sea, carved on a wall in tenth-century Iceland and comprehensible enough to an audience that a skald could allude to it in passing. Norse mythology is full of these craters — the shape of a story is visible, the story is gone.
His kennings preserve another: Heimdall is "the head's bane" and a head is called "Heimdall's sword." Snorri knows a story explaining it and declines to tell it.
Idris Elba and the whitest of the Aesir
Marvel's Heimdall, played by Idris Elba, is the single most visible Norse god in modern media after Thor and Loki, and the portrayal is unusually faithful in one respect — the all-seeing sentinel at the bridge is exactly the source figure — while inventing the loyal-general characterisation wholesale. The casting caused a public argument in 2010 that the sources cannot adjudicate: Old Norse hvítastr ása, "whitest of the Æsir," is his epithet, and hvítr in skaldic usage carries senses of bright, shining and radiant that do not map onto modern racial vocabulary at all.
For where his enmity with Loki ends, see Ragnarök; for the bridge he guards, Bifröst; and for the wider tradition, the Norse overview.
If he hears grass grow, why does he never warn anyone in time?
Because his function is not prevention. Norse cosmology treats the end as fixed and known — the seeress in Völuspá has already narrated it — so a sentry's job is not to avert the attack but to mark the moment. The horn is a clock, not an alarm. Nothing in the corpus suggests any god believes the sounding of Gjallarhorn will change what follows it.
Is there any evidence of a Heimdall cult?
Effectively none, and this is one of the sharper asymmetries in the record. No place-names are securely formed on his name, no personal names, no amulets. He is prominent in poetry — Völuspá names the audience after him — and absent from the ground. Whatever kind of figure he was, he does not appear to have been one people made offerings to, which raises the possibility that he belongs to a poetic-cosmological layer of the tradition rather than a devotional one.