Look hard at this line drawing. To the best of our knowledge, it has never been published before. The subject is Ezra Pound, the rambunctious American poet and poetry impresario who took literary London by storm towards the end of the first decade of the twentieth century. 

The drawing is by Henri Gaudier - better known as Gaudier-Brzeska. Gaudier did a number of drawings of Pound. He also made what has come to be known as a 'hieratic head' of the poet, carved out of white marble. This monumental head, completed in 1914, languished in a Kensington garden for sixteen years before being shipped off to join its subject in Rapallo, Italy, where Pound was cosying up to Mussolini.

Pound and Gaudier were good friends. The American was full of admiration for this fierce young man from France. Pound saw him for the first time at the Albert Hall in 1911. 'He was like a well-made young wolf or some soft-moving, bright-eyed wild thing,' Pound wrote, unusually enthralled. Gaudier, though small and lean, was a bit of a tough guy. He carried chisels in his pockets when he moved about the streets of London - in readiness for being set upon. He and Pound talked a lot together. 'We had long, gay, electrified arguments over my scepticism as to the impracticability of anarchy, over my disparagements of the benefit of living like African tribesmen, however fine their discipline might be for the individual savage.'

The Pound of this drawing shows the poet at an uncharacteristic angle to his own character. It reveals an unusual softness and sensitivity, a yieldingness of temperament. Those are qualities we seldom associate with Pound, who could be a barker - in the way that dogs and The Bow-Wow Shop itself are barkers - and a bully. Its owner, who lives in London, estimates that it was done in 1914, a matter of months before Gaudier's death. It may have been one of the many preparatory drawings Gaudier made for that head. Pound - who could be fairly cavalier with facts - once said that there had been about one hundred of those. In all, about five drawings of Pound by Gaudier are thought to have survived - so the one you can now see here for the first time is quite special. What is more, it is quite different from all the others, which are brisk, geometric and Vorticist in manner. This one seems to have been lingered over a little longer. It is almost tender.

The sculptor Henri Gaudier-Brzeska passed through the art world of London like a comet through the night skies. He arrived in London in 1911. By 1915 he was dead, killed on the Western Front at the age of 23. He had died 'at the beginning of his work,' as Pound, who wrote the first memoir of Gaudier, put it.

Henri Gaudier was the son of artisans from a small village near Orléans. His parents destined him for a life of commerce - but he thought differently. Art was his calling. After arriving in England, he struck up a curious, mother-and-child relationship with a Polish woman he met in a library, Zofia Zuzanna Brzeska. She was twice his age. She called him Pik, Pikus, Pipik; he called her maman, Madka, little Mamus. He tacked her surname onto the end of his. Thus was born the sculptor with the unpronounceable name. Pound tended to call him 'Brzx'  in his private correspondence.

Gaudier's career proceeded by fits and starts. He was desperately poor. He lived in squalid rooms that teemed with mice. He often borrowed, stole or scrounged the materials - odd scraps of marble or alabaster - that he used for his sculptures. He envied cemeteries the marvellous stones that he could see from the top deck of a London bus, just lolling around. The impression he made upon others was often alarming. He seldom bathed. He had a tongue as sharp as one of his own hand-made, well tempered chisels. This is how the writer Enid Bagnold once described him: He was 'more like a dagger in the midst of us. He had a hungry face…and a mind made of metal. He talked like a chisel and argued like a hammer.'

What was the thrust of those arguments? Gaudier thought that the smooth, humanistic naturalism of the Greeks was at an end. The New Art must be archaic, jagged, abstracted. 'I shall derive my emotions solely from the arrangement of surfaces,' he wrote in a manifesto that was published one month after his death. As he sketched Michelangelo's 'Slaves' in the Cast Court of the Victoria and Albert Museum, he scribbled down urgent, serious musings beside his drawings: line, he wrote, is 'an infraction of liberty'; mass, on the other hand, represented freedom.

Unfortunately, there was scarcely world enough or time to carry through his objectives. There are perhaps a dozen works of great brilliance - the squat 'Redstone Dancer' with its marvellous spiralling motion (now in the Tate Gallery's collection), for example - and hundreds - perhaps as many as fifteen hundred, according to a curator we spoke to at the Royal Academy - wonderful drawings, including rapidly caught likenesses of animals which often look as lean, rapacious and determined as the man who drew them. Much of the rest is great promise yet to be fulfilled.

Wyndham Lewis saw Gaudier leaving England for the last time, by boat train, for the Front, and later ruminated upon that poignant departure. 'It is easy to laugh at the exaggerated estimate "the artist" puts upon his precious life,' he wrote. 'But when it is really an artist - and there are very few - it is at the death of something terribly alive that you are assisting. And this little figure was so preternaturally alive…'