The story is told of Marilyn Monroe and a friend walking down Fifth Avenue one day in the 1950s discussing Marilyn Monroe. MM was wearing a headscarf and a plain, belted raincoat. The friend remarked on the great difference there was between the woman he knew and the star the world thought it knew. “You want me to be her?” Marilyn said. “Watch.” She whipped off the scarf, opened the raincoat, thrust out her chest and put on The Walk. Within seconds, she was surrounded by a gaggle of excited fans clamouring for her autograph.

Monroe was one of the 20th century’s great clowns, whose clowning was intended not to make us laugh – though she was wonderfully funny – but to lose ourselves in fantasies of longing and desire. Most movie stars act the part of themselves, more or less convincingly; Marilyn created a wholly other version of herself, meant not to convince but to seduce. She was both Frankenstein and Frankenstein’s monster, and it is our subliminal awareness of this duality that makes her such a fascinating and compelling creature, even still, more than 60 years after her death.

Early in the 1950s, Monroe saw a photo-article by Eve Arnold in Esquire magazine and was impressed. The subject was Marlene Dietrich and, when Monroe met the photographer at a party in New York given by John Huston at the 21 Club (where else?), she said to Arnold: “If you could do that well with Marlene, can you imagine what you could do with me?”. The two hit it off and Arnold was to become Monroe’s semi-official “court photographer” for the rest of her short life.

It is not special pleading on Arnold’s part when she claims that Monroe took still photography as seriously, if not more so, than film. The inimitable wiggle that she put on for the movie camera – “like Jello on springs”, as the Jack Lemmon character has it in Some Like It Hot – had its statuesque form in the poses she struck for the photographer’s lens. However, she had liked the Esquire shoot because it was, as Arnold writes, “a departure from the carefully lit, posed and retouched genre of movie-star studio portraits”.

All the same, she was very choosy indeed when it came to the images she would allow to be printed. In Marilyn Monroe – originally published in 1987 and now reissued in a revised edition with newly mastered prints by Danny Pope – we hear of her vetoing shot after shot if they did not come up to her standards of glamour and gorgeousness. “She was quick and perceptive,” Arnold notes, “would listen when I explained why a certain picture or situation was necessary, and would concur if she was convinced. If not, we would battle it out until one or the other backed down.”

How did she get away with flaunting such raw sexuality? For no amount of airbrushing or euphemistic costuming could hide the fact, amply attested to in Arnold’s photographs of her, that this was a real woman, with a shape – slightly dumpy, with plump thighs and a big bum – not all that much different from that of your mother, or your wife, or that girl down the street you always fancied. A large part of her attraction for men, and probably for women, too, was that she was ordinary, and yet a phantom out of the sweatiest of night-time dreams.

Her looks were not remarkable: no one with a nose like that could be described as a classic beauty – and the bone structure of her face was weak. When she was not “being” MM, many of the people she met did not recognise her and refused to believe she was Marilyn. Yet, when she was in front of the camera, she was luminous. “Up close,” Arnold tells us, “around the periphery of her face there was a dusting of faint down. This light fuzz trapped light and caused an aureole to form, giving her a faint glow on film …”

She knew from the start how vital to her success still photography would be; the photo magazines of the 1950s and 60s sold in the millions. By the time she met Eve Arnold she was a star, and could afford to relax, at least a little way, into being herself, even if she no longer knew exactly where the self gave way to the image.

There are some wonderfully intimate, tender and witty photographs in this big sumptuous volume, as well as ones that capture, as only the still camera can, the insecurity and pain behind the ever-smiling facade. In Arnold, both Marilyn Monroe and Norma Jeane Baker found their ideal imagist. As Arnold said: “If a photographer cares about the people before the lens and is compassionate, much is given. It is the photographer, not the camera, that is the instrument.”

• Marilyn Monroe by Eve Arnold is published by ACC Art Books (£40). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply