Heimdall is the god of guardianship in Norse mythology. He is the keeper of the realm of the gods and guards the Bifrost bridge. His senses are so acute that he can hear grass growing and his need for sleep is reduced beyond the least imaginable, so that there is no need for other guardians for the Bifrost except in the case of his absence (normally to accompany Odin or Thor himself). Heimdall carries his magical sword Hǫfuð with him.
Heimdall is the elder brother of Sif, Thor's wife, and one of the main Norse gods. He was the son of nine different mothers and Odin, probably the nine daughters of Ægir, identifiable with the cycles of waves, and was the keeper of the bridge Bifrost, along with the rooster Gullinkambi, and the possessor of the horn Gjallarhorn, which would transmit the signal of the arrival of the enemies for the final battle of Ragnarok for all of Asgard and up to the halls of Valhalla.
Nicknamed the White God, father of all men: slaves (thrall), freemen (karl) and nobles (jarl), had from the three unions with mortal women of different ages, loveliness and lineage, he is identified with the ram, whose horns adorned his helmet. His hall was called Himinbjörg (protection of heaven) and his horse was Gultopp (in English Gold-top).
To make him insensitive to remote magic, he was subjected to a series of initiation rites. The guardian of the bridge of Bifrost, which connects Asgard (residence of the gods Æsir and Vanir) to Midgard (residence of men), is not only the one who, thanks to his overdeveloped senses (hearing and sight) (120 leagues is the distance from the edge of the battlefield where, at the beginning of Ragnarok, the infernal hordes of Muspellheim, led by Loki, will appear), will warn the Æsir of the arrival of the enemy, but it is also the one who, in the final battle, will kill Loki in combat, being in turn killed, while Thor will have the task of killing Jormungrandr, otherwise known as the Midgard Serpent and son of Loki, who will come out of the ocean waters after having surrounded with its coils the edge of the earth and marked the boundaries of the sea.
He is the symbol of the loyalty and devotion of the warrior, as well as the progenitor of mankind and of the social order of the Norse and Germanic people.
Snorri Sturluson's prose Edda reports that a synonym for sword is Heimdall's head, because Heimdall was struck by a man's head; this is treated in the poem Heimdalargaldr, of which unfortunately no copy exists anymore. Similarly, a synonym for head is sword of Heimdall.
The meaning may be that Heimdall was also called a ram, and the weapons of a ram are its horns and its head. Georges Dumézil in 1959 suggested that this may also be why Heimdall was called the White God (white like the fleece of the ram, but also like the foam of the waves).
Heimdall's nickname Hallinskíði (bent staff) appears as a synonym for "ram," perhaps referring to the ram's horns being bent, curved in on themselves.
Another alias for Heimdall was Gullintanni (golden teeth) may refer to the yellow color that the teeth of old rams take on, but also to the reflection of the light of the firmament on the Bifrost bridge. Dumézil cites Welsh tradition that says how the waves of the ocean come in groups of nine and that the ninth is the ram:
"We understand that, whatever its mystical value and functions were, the environment of its birth made it what it is, the white foam of the sea, the ram produced by the ninth wave. If this is so, then it is correct to say that he has nine mothers, for one is not enough, nor two, nor three."
The ancient Welsh, and modern French (Breton and Norman) and Basque practice is to call the waves with the white foam sheep, or, in the Franco-Norman tradition, "moutons" (rams) precisely with reference to the ninth wave, the ninth mother necessary for the completion of Heimdall's conception and generation as described in the sagas.