The sidewalk vendors of Times Square sell cheap metal signs bearing the image of Spider-Man, no doubt unaware that the superhero’s co-creator walks right past them every day, completely unrecognized.

Then again, only a handful of people in the world would recognize Steve Ditko, the mysterious 84-year-old artist who, with writer Stan Lee, dreamed up the wall crawler back in 1962.

Ditko has long been thought of as the J.D. Salinger of the comics world. He has not given a formal interview since the 1960s — and even back then, he would often respond to a journalist’s questions via mail. Only a few public photographs are known to exist of him, the last taken in his dingy Hell’s Kitchen studio 53 years ago. He lives a rigorously private life, refusing to appear in public, to autograph work or to take a casual snapshot with a fan, should one somehow manage to track him down.

He never married, never had children. He was never particularly close to anyone with whom he worked. He has been called “impossibly uptight” by fellow comic book writer Neil Gaiman. The only thing Ditko ever seemed to care about is the Work, and to this day, even well past retirement age, he continues to turn up every weekday at his Midtown West studio and put in eight hours of drawing. Sitting alone behind a windowless steel door with a nameplate reading “S. Ditko,” the artist, who long ago left mainstream and superhero comics behind, creates strange, self-published comic books often steeped in the Objectivist philosophy of Ayn Rand, of whom he is a devoted adherent.

And those hoping that the opening of today’s “The Amazing Spider-Man” will draw him into the public eye will be sorely disappointed.

When The Post knocked on his door, Ditko — who turns out to be a owlish man with wisps of white hair and ink-stained hands, wearing large black glasses and an unbuttoned white shirt with a white tee beneath — pleasantly but firmly declines to answer any questions. Though he did say he reads The Post.

“I don’t have anything to say,” he says, standing in the doorway to his studio. Rumors abound that he also lives there, but a source in the building says he might be living at a nearby hotel.

“He’s never been interested in celebrity, and he’s obviously at peace with it,” says Blake Bell, author of “Strange and Stranger: The World of Steve Ditko.”

“He could have made a big stink, especially when the first ‘Spider-Man’ movie came out [in 2002], and he probably could have gotten a lot of money and publicity, but he didn’t.”

Steve Ditko was born in Johnstown, Pa. He moved to New York in 1950 and began drawing comics, mostly horror and sci-fi. It wasn’t until he hooked up with Marvel Comics and Lee in 1955, however, that he took a step toward becoming a legend.

The creation of Spider-Man is muddied by the years, conflicting points of view and the fact that no one involved paid much attention at the time because they never thought the adventures of a teenager who gains the powers of an arachnid would amount to anything.

What we do know: In 1962, Lee, the co-creator of the Fantastic Four and Iron Man, had an idea for a new hero and passed a synopsis on to artist Jack Kirby. The story involved a teen who gained spider powers via a magic ring. Lee was underwhelmed by Kirby’s overly heroic take and went to Ditko.

Not only did Ditko design the iconic costume, he may have contributed many of the elements that have made Spidey so popular over the decades. Unlike the godlike other heroes of the time — Superman, for example — Spider-Man and his alter ego, Peter Parker, had very human, relatable problems.

“Ditko took what was a very good superhero comic strip and really turned it into something revolutionary,” Bell says.

“It was Ditko who wanted to ground the strip in reality, to see what it was like to be a hero through the eyes of a teenager and to struggle.”

The direction put Ditko at odds with Lee, but because the writer-editor was so busy running Marvel, he increasingly turned over more story control to Ditko. By about issue No. 10, the artist was also plotting the stories, with Lee just filling in dialogue after the pages were drawn. By No. 25, the two were no longer speaking. Bucking the comic-book formula of the day, Ditko focused less on action scenes involving Spider-Man and more on the troubled life of Parker.

“The Amazing Spider-Man” No. 18 featured almost no costumed Spidey. In a letter column run in other Marvel books at the time, Lee took a jab at Ditko, writing, “A lot of readers are sure to hate [No. 18], so if you want to know what all the criticism is about, be sure to buy a copy.”

Spider-Man ultimately became a giant hit, but with issue No. 38, Ditko quit, reportedly walking away with no notice. Bell says the artist was angry with Marvel Comics for failing to deliver on promised royalties.

To this day, Ditko has probably made very little off his billion-dollar co-creation. He has no ownership of the character and was paid a modest per-page rate at the time. He does collect royalties each time the comics are reprinted, but he says he has not earned anything off the films, despite his name appearing in the credits.

“No,” he tells The Post, when asked if he was paid anything for the four recent Spider-Man movies.

“I haven’t been involved with Spider-Man since the ’60s.”

Whatever the case, the artist doesn’t seem much interested in money. Although he could make thousands doing commissions for fans, he consistently refuses. Instead, he forges ahead on black-and-white, self-published books with titles like “The Avenging Mind.”

“I do those because that’s all they’ll let me do,” he tells The Post, suggesting big publishers aren’t interested in his work anymore.

Then there’s the matter of the original art he created for his “Spider-Man” run. When Greg Theakston, an artist and the editor of several Ditko books, visited the artist in his studio in 1993 to discuss a project, he saw huge stacks of Spidey pages gathering dust that could be potentially worth millions. Ditko was also using some of the art as a cutting board. Horrified, Theakston offered to buy Ditko a new cutting board, but Ditko refused with a terse “no.”

“He drew those pages because he liked to draw comics, not because he was getting paid or published,” Theakston says.

The artist seems to live his entire life by a rigorous code, much of it shaded by Objectivism, which posits that “productive achievement [is man’s] noblest activity and reason his only absolute.”

Tom DeFalco, a writer and the editor-in-chief of Marvel Comics from 1987 to 1994, was paired with Ditko, whom he’d never met, on the 1979 series “Machine Man.” After the Marvel offices forwarded DeFalco’s plot outline to Ditko, the writer’s home phone rang.

“I picked it up, and this voice says, ‘Are you Tom? What gives you the right to write about heroes?’ ” DeFalco recalls.

“I said, ‘Who is this?’ He said, ‘This is Steve Ditko.’ ”

The two discussed the nature of heroism for an hour and a half. DeFalco says the artist loved debating, but the two never talked about personal lives.

Ditko has fallen out with many of his colleagues over the years because of conflicts or perceived slights. He no longer speaks to Stan Lee because in 1999, Lee wrote an open letter assigning Ditko half of the credit for creating Spider-Man, saying he “considered” Ditko to be the co-creator. Ditko took issue with the word “consider,” and that was that.

He has broken off contact with publishers over printing errors. He was reasonably friendly with Bell until “Strange and Stranger” was announced. Although he hadn’t seen the book, Ditko called it a “poison sandwich” and hung up when the publisher called to soothe him.

“Just having a conversation with him is difficult,” says Craig Yoe, author of the forthcoming “The Creativity of Steve Ditko,” who had lunch with the artist in the early 1990s.

“There wasn’t an easy exchange or even polite conversation. Every reply would be some strong philosophical answer.”

Yoe casually asked Ditko about autographing a piece of art, and the artist responded with a thoughtful tirade that it was morally wrong to sign artwork, because that’s not the intention of the artwork; it’s meant to be reproduced in a magazine.

Long ago, Ditko explained his reason for staying so private, Bell says. “He said, ‘I never talk about myself. My work is me. I do my best, and if I like it, I hope someone else likes it, too.’ He’s a genius, and geniuses are often quirky,” Yoe adds. “He’s allowed to be quirky — this is America.”

Here’s hoping that with the release of “The Amazing Spider-Man,” this quirky genius finally gets more of his due. reed.tucker@nypost.com