AS A SMALL CHILD I spent Hitler’s war reading an adult book by a German – Asgard and the Gods by Dr W. Wägner, published in English in 1888 with wonderful mysterious engravings of strange worlds, monstrous creatures and wild battles.

My mother had it as a crib for her Ancient Norse and Icelandic studies at Cambridge. It was – and is – my favourite book. I responded to that world and those tales as I never responded to Christianity or the Greeks. I liked the image of the World Tree, gnawed by a rat and a worm. I responded with passionate excitement to the idea that the gods could die, that the end of the world would come, and nothing at all would be left. I still do.

Heather O’Donoghue is a reader in Ancient Icelandic literature in Oxford. From Asgard to Valhalla is an account of how the Nordic myths came to us, and of their reception – from early Christian interpretations to virtual games, graphic novels and Swedish and Norwegian Viking heavy metal music.

She begins with Christian Iceland, and Snorri Sturluson in the 13th century collecting myths and poems into what we know as the Prose Edda. The Icelanders, in 1000AD, made a democratic decision to become Christians, and abandon the old beliefs, which nevertheless persisted, and persist.

Snorri, she says, treats Odin and the other gods as humans grown into gods, or gods with human characteristics. There is a complex relationship between the stories of the gods' humours, failings, jealousies and folly and the stories that have come down to us of Odinic rites, including bloody sacrifice. Famous lines in one Eddaic poem describe Odin hanging on a tree:

wounded with a spear, dedicated to Odin, myself to myself, on that tree of which no man knows from where its roots run . . .

This image connects the Nordic Allfather with Christian sacrifice, and Ragnarok, the Last Battle, with the Cross. Such connections run through carvings in churches and on gravestones. Snorri’s account of Ragnarok, in which monsters and flames destroy Earth, gods, Sun, Moon and stars, ends with the return – after a long period of dark and emptiness – of a new Heaven and a new Earth. It has been suggested that this was taken from the Christian Apocalypse. I like to think that the Norse ending was harder and more final.

O’Donoghue is not as exciting as Dr Wägner about the old tales. She promises to tell us about Norse elves who are “chillingly shadowy beings”, and never does. But she is good – and to me, surprising – on Romantic versions of the myths, from Percy’s Northern Antiquities to Walter Scott and Southey. Thomas Gray, of the Elegy Written in a Country Churchyard,wrote Norse Odes that seem to have been vivid and blooodthirsty, grim and atmospheric. He appears to have introduced the word Valkyries into English, and his fatal sisters – an amalgam of Norns, Valkyries and the Greek Fates – weave a “web of death”: See the grisly texture grow (’Tis of human entrails made) And the weights that play below Each a gaping warrior's head.

The Romantic Nordic imagery gets into visual art – O’Donoghue reproduces Fuseli’s atmospheric painting of Thor battering the Midgard serpent. William Blake illustrated Gray’s Fatal Sisters and the Descent of Odin in 1797, and wrote in Jerusalem of Norse gods as the barbarous enemy of a Saxon paradise: Woden and Thor and Friga wholly consume my Saxons On their enormous Altars built in the terrible North.

O’Donoghue discusses Richard Wagner’s use of the myths in the Ring cycle, and the connection of this to the “rise of racism” and the use of myths and images in cults of Germanic or Nordic racial purity. Reading this book illuminates the problem that Wagner solved brilliantly – of how the gods of Valhalla are simultaneously powerful controlling deities, and quarrelsome, sometimes trivial, shortsighted humans.

This is, as O’Donoghue sees, a problem with all personified deities – and is part of the essence of the Norse stories, entwined as they were, from our first knowledge of them, with Christian rationalisation.

O’Donoghue says in her discussion of the cosmic myth that the World Tree makes the cosmos an organism; Wagner’s World Ash, and its burning, are the mythic centre of the operas. Wagner’s additions to the stories are compelling. They include Wotan’s spear, ripped from the World Ash and covered with treaties in runes, and the destruction of Valhalla in fire rising from the dead branches of the World Ash. The birth of Siegfried, like other heroes in myth born from incestuous twins, holds, as O’Donoghue points out, an attraction “for those predisposed to value racial purity”. She documents the exclusive societies, much concerned with the symbolism of runes, which fed into use of the “S” rune by the SS.

Exclusive societies such as the Edda Society and the Thule Society spread occult ideas based on the old myths. She tells us that “the patterns of wooden beams on the outside of half-timbered houses, secretly expressed Aryan esoteric wisdom”. This came as a revelation about the grim art of the contemporary German painter Anselm Kiefer, with his wood-beamed attics, burning like Valhalla.

O’Donoghue does not mention Kiefer, but the ferocity and complexity of his use of this material is one of its most exciting and modern manifestations. She discusses Tolkien meekly and perfunctorily, but is good on Neil Gaiman’s wild and popular American Gods, with his Mr Wednesday and modern Ragnarok. She is also good on Diana Wynne Jones’s children’s tale of Loki, who “meets Just William” in Eight Days of Luke.

A book that she does not mention is The Downfall of the Gods by the Danish author Villy Sørensen. Sørensen tried to retell the tales of Baldur, the Fenris Wolf, the World Serpent and the loves of the gods, in a “human” way, to strip the tales of their grandiose Wagnerian and Nazi connotations. But it is an odd read. You can feel what is missing in every line. Gods are not human, and a myth is a myth – full of riddles, apprehension and spare meaning – or it is nothing. O’Donoghue’s book helps us to understand this problem.

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