When Andy Warhol died 20 years ago, he had become famous in every field he entered: commercial art, painting, film, photography, sculpture, publishing, music and collecting. Even if some people today are not sure exactly what he was famous for, his name and his face are everywhere in our culture – a sort of inscrutable, silver-wigged media mutant, an ageless Pop star, a celebrity on the scale of his subject, Marilyn, and the most famous artist since Picasso. This May, Warhol’s 1963 painting Green Car Crash sold at auction for $71.7 million.

A major exhibition at the Royal Scottish Academy marking the 20th anniversary of Warhol’s death displays the range and versatility of his work – and the extent of his workaholism. Warhol was driven to work, constantly interpreting everything he saw around him and, in the process, transforming the way we see the world around us. But his ultimate goal was fame. As the American art critic Dave Hickey explained in Ric Burns’s excellent Warhol documentary, “He wanted to be very famous. It was very important to him. To succeed. It was a mode of survival. He was really driven. I don’t think he spent an hour of his life without thinking about how to make it work.”

In the end it worked more effectively than he could have dreamt, as the Edinburgh show demonstrates, with a broad range of Warhol’s work from the Forties to 1986, covering painting, sculpture, film and photography. But the area of his life richest in revelation is the period between his arrival in New York in 1949 and his breakthrough in 1962, with the exhibition of his Campbell’s Soup paintings.

Those first 13 years in New York he spent working overtime as a commercial artist, struggling initially to pay the rent, while developing ideas, honing his skills, pushing artistic boundaries and laying the foundations for the avant-garde work that was to come. During those years, he rose to the top of the commercial art world, becoming the highest-paid artist in his field, with enough money to buy a four-storey house on Lexington Avenue. He began collecting art, picking up works by Picasso, Magritte, Klee, Braque, Miró. Yet he wanted more. He wanted to be world famous, and he knew that there is no such thing as a world-famous commercial artist.

Warhol himself would gloss over those early years, perhaps because they were most revealing of the man. In contrast to the impenetrable Warhol of later years, this early period reveals him as a fellow human being, someone we might recognise and understand: an awkward and short-sighted young man, from a poor immigrant background in Pittsburgh, whose father had died when he was young. He longed to befriend celebrities, but the man who would later be friends with Bianca Jagger and Jackie Onassis found himself universally shunned by New York’s elite.

“He was ethnic Polish with a bad nose and blotchy skin,” says the American writer Wayne Koestenbaum. “He was gay, with a freaky mother, bad with people, probably dyslexic, a little autistic. He might even have had Asperger’s Syndrome or that kind of thing.” Warhol had thick glasses, thinning hair and an inferiority complex. “He just wasn’t handsome,” recalls Anthony d’Offay, curator of the Edinburgh exhibition. “He wasn’t sexy. He didn’t look healthy. I remember being stuck in a lift with him once and looking at that pallid skin, covered in powder, and thinking, ‘This is the image of death.’ All his life he was worshipping people. He later became an enormous star himself, but he continued to act like a teenager.”

A few months after he had arrived in New York and begun making a name for himself in magazine illustration, Warhol saw the photograph of Truman Capote on the dust jacket of his book A Tree of Night and was fascinated by the image. He became infatuated by the author. He wrote him hundreds of fan letters, hung around his home. He wanted everything Capote had: blond good looks, fame, verbal powers, precocity. He wanted to be Capote. He sat in the Palm Court of the Plaza Hotel, hoping to be mistaken for the acclaimed young writer. But Capote was repulsed by the attention and ignored the torrent of messages. “As far as I know he’s just a window decorator,” he commented to a friend. “One of those hopeless people you know nothing is going to happen to. Just a born loser.”

Warhol would move on to new idols. He got himself invited to a picnic with Greta Garbo. He was too shy to speak, so he drew a butterfly and handed it to her. “She looked at it bemused,” recalled another guest. “At the end of the day, she absent-mindedly crumpled it and left it behind. Andy picked it up and had his mother write on it, ‘Crumpled butterfly by Greta Garbo’.”

Meanwhile, Warhol was doing well in his career. His draughtsmanship was brilliant, he was intelligent, adaptable and fast – an art director’s dream. His range was enormous. For Bergdorf’s he made Christmas cards. For New Directions he designed book jackets. For Bonwit Teller and Tiffany he created window displays. He did album covers. In 1955, he became the regular illustrator for the shoe ads that I. Miller placed in The New York Times. His style of bright colours and blotted line printing became the symbol of all that was sophisticated in commercial art. He won awards and prizes and, at the end of 1957, to his great delight, was listed under “fashion” in a book called 1,000 New York Names and Where to Drop Them. Every advertising agency in town was hot on his trail.

This is not surprising, because Warhol’s early work is beautiful. He made thousands of charming line drawings, of cherubs, butterflies and flowers, washed with bright colours. These were gentle pictures, accessible and full of emotion, the creations of a gifted artist with his own vision of what constitutes beauty. He also worked in every spare hour in his private world, doing thousands of homoerotic line depictions in pencil or ink of beautiful young men, and deft drawings of children, cats and cakes. He did a series of illustrations for a book of absurd cooking recipes, and shoe drawings coloured with gold leaf. His mother, who had moved from Pittsburgh to live with him “until he found a nice girl”, did the loopy writing on all his drawings and the texts on his commercial assignments. She even signed his name.

But these whimsical projects, like his commercial work, were not large enough for his talent and ambition. He wanted to be a fine artist. And a famous one. In Fifties New York, nobody in the fine-art world wanted anything to do with commercial art. The art style of preference was abstract expressionism, personified by Jackson Pollock. Pollock and friends were tough, hard-drinking heterosexuals. Andy Warhol was a shy, diffident homosexual. Everything about his style of art doomed it in the world of fine art.

In the late Fifties, the Bodley Gallery showed some of Warhol’s shoe pictures and drawings of young men, without acclaim. In 1956, an ice-cream parlour on the Upper East Side, a meeting place for gay men, showed his Drawings for a Boy book. Not one sold. “Oh my God,” he lamented. “Bombed again.” In 1958, Jasper Johns had a show at the Leo Castelli Gallery, of images of everyday objects. The show sold out. The following year, his partner Robert Rauschenberg had a successful show of pictures derived from street signs. The fortress of abstract expressionism was being breached and the Pop Art style was emerging.

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