Ed Ruscha strikes most people who meet him as the quintessence of what they imagine the contemporary Los Angeles artist should be like. He’s a man — as is evident in a 1964 photograph by Dennis Hopper of the young artist standing in front of a neon shop sign that reads “TV Radio Service” — who has always come across as self-assured but unpretentious, easy in his skin, good-looking, well-edged features, wry, cool, laconic, yet somehow slightly disengaged. Hollywood central casting could have done no better. It’s not surprising that he has at times been linked, as they say, to models and actresses.

Yet early in his career, Ruscha was keen to disavow the influence of Los Angeles, his adopted city. “Being in Los Angeles has had little or no effect on my work,” he insisted. “I could have done it anywhere.”

That statement now seems as modestly surprising and provocatively ironic as his best work, much of which can be seen in a big retrospective, Fifty Years of Painting, at the Hayward in London. Ralph Rugoff, the gallery’s director, believes the show cements Ruscha’s reputation as “one of the most innovative and influential American artists of the past half-century”.

The film-maker David Lynch, a great admirer of Ruscha, who also adopted LA as his home and has offered his own interpretations of it in films such as Mulholland Drive and Inland Empire, admits he is a bit perplexed by Ruscha’s assertion. “Ed has said California hasn’t influenced him one little bit, but I disagree. I like to think the California sun has burnt out all unnecessary elements in his work.”

The bigger truth is that you can’t look at a lot of Ruscha’s paintings without thinking of LA, “with its sign-filled streets sprawling like dispersed and diffused flows of random information”, as Rugoff notes in his catalogue essay. (Ruscha, by the way, once had business cards printed to aid in the pronunciation of his name: “Ed-werd Rew-shay”.) What’s more remarkable, and indicative of his importance, is that because of the extraordinary impact his artistic reconstitution of his adopted city has had on the wider cultural world, you can’t really understand LA — or perhaps any contemporary American city — without knowing you’re at least partly seeing it through the eyes of Ed Ruscha. The novelist James Ellroy, LA born and bred, calls him “the visual deus ex machina of what has become the most overscrutinised city on earth”.

What’s most likely is that in 1966, when he made that statement, Ruscha knew it wasn’t in his interest to be pigeonholed as an LA artist, because LA was still considered an artistic backwater. Ruscha had driven out there in 1956, when he was 19, from the midwestern city of Omaha, Nebraska, where he had grown up — his father was an auditor with an insurance company there — to study graphic design at the Chouinard Art Institute. And to escape his austere, repressive Catholic background. “The biggest thing I learnt in art school was that I had to unlearn everything I’d learnt before — since my birth, literally,” Ruscha later said.

The vitality of the LA art scene that he quickly found a place in, working for a while in a printing house and an ad agency, came in part from its distance from New York, the epicentre of the art world; from the prevailing theology of abstract expressionism and the commercialism of the big galleries there. That allowed LA artists such as Ruscha, Ed Kienholz, Ed Moses, Robert Irwin, Larry Bell and Billy Al Bengston — loosely known as the cool school — the freedom to play with ideas and forms that soon became a distinct stream of pop and conceptual art. Most of the leading LA artists were represented by the Ferus gallery, which, despite its West Coast setting, was the first anywhere to show Warhol’s soup cans. Ruscha had his first show at Ferus in 1963.

For him, the experimentation began to take the form of words. Whereas abstract expressionism was in great part about the act of creation, for Ruscha “premeditation” became more important. “It’s the end product I’m after,” he said. In what became a trademark, many of his paintings from the late 1950s into the 1960s and beyond used words — first single words; later phrases and sentences — as artistic objects. Like Warhol’s soup cans, they could be seen — for instance SPAM (Actual Size, 1962) — as polemic riffs on advertising and mass consumption. Yet Ruscha, with his background in graphic art, was never trying to make political or social points. For him it was about the look, the form of the letters and even, with word paintings such as BOSS, OOF and HONK, the sound behind the form. “I see words as objects,” he always insists. “I am painting pictures of objects.”

Lynch loves Ruscha’s transformative use of words in painting. “The words are made up of letters,” he explains, in a way that we once all knew as children. “A letter is a shape, and a very interesting shape. He uses these letters as shapes, and that’s very, very beautiful. And when you know the meaning, when the letters come together and form a word, then that’s a whole other level, and it kicks in a thinking process, and feeling, too. So it gets thinking and feeling going in a minimal, beautiful way. His work is painterly; it’s not a billboard, it’s painterly. And that’s super-important.”

Why super-important? “Because there’s this painterly thing that puts Ed in the painting: a human being, working with the paint. It’s a texture that gives a feeling that is not computer-generated. A human being did this. Ed.”

Ruscha had an obvious effect on the next generation of LA artists, such as Mike Kelley and Jack Pierson. But his influence, as anyone walking round the Frieze show could see, has been far more widespread. Take Gabriel Kuri, a young Mexican artist who divides his time between Mexico City and Brussels, and was showing at Sadie Coles’s Frieze stand. “Ed Ruscha has been one of my heroes, always,” Kuri says. “He is an intuitive master at picking a word or phrase from a larger context — a conversation? A book? Movie? Unconscious? Dustbin of oblivion? — and reinvesting it with significance. You can really chew on his word paintings for ever, and they never run out of gist. Super-simple, yet you can never quite work him out.”

Part of that simplicity has come from Ruscha’s deliberate promotion of what had always seemed banal and uninteresting. “I’m interested in glorifying things that we in the world would say don’t deserve to be glorified,” he has said. Take his numerous reworkings of Standard gasoline stations, which started with a series of apparently banal, even uninteresting black-and-white photographs of petrol stations he had taken along Route 66. The word “Standard” is key in its lack of affect. They appeared first in his 1963 artist’s book, Twentysix Gasoline Stations, spilling over into his painting in powerful works such as his Standard Station 1966, an image that looks like a logo for an as yet unincorporated Hollywood studio financed by an oil company (as some have been).

Twentysix Gasoline Stations — utilitarian and deliberately depersonalised — has had a profound effect on modern art and photography, most obviously in the work and teaching of the most influential contemporary photographers, Bernd and Hilla Becher. Ruscha took the idea of the photographic series further with his 1966 book Every Building on the Sunset Strip, a panorama of both sides of the famous street in West Hollywood. To take the pictures, Ruscha mounteda motorised camera on the back of a truck, a mechanical device intended to strip the work of personal input.

Ruscha has always insisted: “My pictures are not that interesting, nor is the subject matter. They are simply a collection of facts.”

“I think that’s baloney,” Lynch says with a laugh. Well, Spam, perhaps. Before Ruscha, such objects — words, gasoline stations, street frontages — were not seen as interesting. Now, because of him, we can see even gasoline stations as having “angles, colours and shapes, like trees”, as the artist has put it, capable, in his hands, of epic re-presentation.

Despite having met Ruscha a few times through the actor Dennis Hopper, Lynch says he has never had a proper conversation with him. I wonder what he’d like to talk to him about. “Well, you know, his studio, what kind of setup he’s got. What time he starts working. Does he drink coffee?” (Lynch is known to be a monumental coffee drinker.)

And how would Lynch describe Ruscha, as a human being? “Clean!” he immediately shoots back.

CLEAN. Is that a Ruscha word painting? CLEAN.

Ed Rushca, Hayward Gallery, SE1, until Jan 10

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