WE know what is usually meant by the word in the subtitle. It's taken to mean that the subject has not approved, assisted or blessed the project and might even have tried to thwart it, though that more often happens to biographies with "scandalous" or "intimate" in the billing. In the context of Jonathan Bate's massive and detailed study of a man whose intimacies and scandals have already been picked over many times, "unauthorised" refers as much to the life as lived as it does to the life as written.

Ted Hughes lived according to no authority other than his own, and that of the shifting, eternal Goddess who was the object of all his quests, sometimes filtered through the iconography of Shakespeare, sometimes represented by a wife or lover. His relations with women, as his fiercely intelligent sister Olwyn once said, was that by trying not to hurt anybody, he always managed to hurt everybody. Mother, wives, mistresses, sister/agent/confidante, all seem to combine into a mythic semi-person that is not so much idealised and put on a pedestal as continually violated by small acts of neglect or cruelty, much as the Goddess is mildewed and bruised in contact with real life.

A stray reference by the most celebrated of those women to the unnamed Hughes as "sadistic" has propped up his unfair reputation as English poetry's Bluebeard, or as Norman Mailer with an "ee bah gum" accent. Interestingly, Hughes uses the same word for his own university skill at practical criticism. Most who report the former reference fail to consider the possibility that Sylvia Plath was simply a compulsive self-dramatiser, or in more literary terms that she was far from the "autobiographical" and "confessional" poet we've learned to accept and instead someone who erected her own mythologies, of which Ted was a part.

Inevitably, any biographer of Hughes - and Bate isn't the first - has to deal with the weird lensing effect of those few, intense years of marriage and his lasting status, neutral to hostile, as Her Husband. Bate deals with those years briskly and almost entirely in the context of a shared writing life, during which Hughes showed a gawky co-ed how to send down a bucket into the unconscious and how to deal with what came up in it. He views Hughes's own life, if it can be detached at all from the conjugal tangle (and the late appearance of Birthday Letters suggests it can't), under the aspect of the poetry and prose that came out of it.

The view of Sylvia as an over-sharer, and Ted as a mythic giant who simply gathered tribute from his satellites and gave out gnomic mutterings in return is quite wrong. Hughes's whole project was to tie together the two strands that propel all of modern British poetry, the twin lines of Wordsworth and Coleridge, the first an attempt to locate the individual soul in the presence of nature, the second to make myths out of ordinary experience, the first public – and Wordsworth was an earlier Poet Laureate – the second intensely inward. The life began under the crag at Mytholmroyd and in the "happy valley" of Crimsworth Dene. Bate shows how the Hughes brothers' early obsession with nature, shooting it first, then studying it, then taking it deep inside as Pike, Hawk, Fox, ultimately Crow, supplied the poet with a subject matter that went beyond humanism and a verse that avoided common sentiment, sometimes too assiduously.

Bate is perfectly candid in admitting just how bad some of the work is. Hughes had his E. J. Thribb (aged 17 1/2) side and remains one of the most easily parodied of modern poets: "Lamb guts on lonely crag / Broken line / No verb". And yet, parody is always a sign of admiration and part of Hughes' great courage – shared with most towering artists, from Picasso to Bob Dylan and even Hugh MacDiarmid – lies in a willingness to throw up lots of smoke and ash along with the magma and to make us participants in the effort to locate it. It is one of the great bodies of poetry from the 20th century.

Quite how great is a matter for longer posterity, but a photograph from 1960 and from a Faber party around the time of Lupercal's publication shows the young Ted in company with Louis MacNeice, T. S. Eliot, W. H. Auden and Stephen Spender; no sign of Larkin, who may have been refreshing his glass somewhere, but Larkin, Hughes's opposite or awkward twin in so many respects, is shown in another picture from 1977, with glass inevitably in hand. They all drank deep of something, these poets, but Hughes's sheer physical force and presence somehow stand out. Eliot is even standing on a stair step to match the height of his young Faber rival.

Three years after that photograph, Sylvia Plath ended her own life and handed Hughes the villain role in a bizarre feminist pantomime that has seen Plath's acolytes chiselling her married name from the gravestone and Hughes booed at readings and lectures simply for possession of a penis. He managed, magnificently on occasion, to rise above it, and rose higher than almost any of his peers, becoming the most intimate of Laureates, whose poetry extended beyond verse to fly-fishing chest-deep with the Queen Mother and talking quietly to the Heir Apparent about the powers in and behind nature. An extraordinary life deserves an extraordinary life, and this, authorised or not, is it.