Steve Ditko, who co-created the Spider-Man and Doctor Strange characters for Marvel Comics, has died at the age of 90, police in New York said.
Lieutenant Paul Ng said Ditko was found on June 29 in his Manhattan apartment and was pronounced dead at the scene.
No further details were immediately available.
Ditko, along with Stan Lee, introduced the world to Peter Parker, and his alter-ego Spider-Man in 1962 in an issue of Amazing Fantasy.
A year later, Ditko introduced the world to surgeon-turned-metaphysical superhero Doctor Strange.
The adventures of Spider-Man and Doctor Strange have been turned into blockbuster films.
Dan Buckley, president of Marvel Entertainment, said: “Today, the Marvel family mourns the loss of Steve Ditko.
“Steve transformed the industry and the Marvel Universe, and his legacy will never be forgotten.”
While Lee embraced his status as a creative god among comics fans, appearing at conventions and in constant cameos in Marvel’s films, Ditko was a recluse who won the worship of the most hardcore comic-book geeks.
They were quick to praise him and the massive influence he had on art, film and culture.
“Thank you Steve Ditko, for making my childhood weirder,” fantasy author and graphic novel author Neil Gaiman said in a series of tweets to his 2.7 million followers.
“He saw things his own way, and he gave us ways of seeing that were unique. Often copied. Never equalled. I know I’m a different person because he was in the world.”
Edgar Wright, director of movies including Baby Driver and Shaun Of The Dead,” said on Twitter that Ditko was “influential on countless planes of existence”.
“Comics are unimaginable without his influence,” tweeted Patch Zircher, a comic-book artist who has worked on Batman and Superman for DC Comics.
“He co-created Spider-man, which will be remembered as significant as Doyle creating Sherlock Holmes or Fleming creating James Bond. Spider-man may outlast them both.”
TV and radio host Jonathan Ross tweeted that Ditko was “the single greatest comic book artist and creator who ever lived”.
The son of a steel-mill worker, Ditko was born in Johnstown, Pennsylvania, in 1927. He served in the army in Europe after the Second World War and began working in comics in the 1950s in New York, eventually landing a drawing job with Marvel forerunner Atlas Comics.
Jack Kirby, Lee’s artist on the Fantastic Four and many other Marvel characters, took a stab at creating Spider-Man in 1961, but Lee was unsatisfied and gave the gig to Ditko, who gave Spidey the essential look he still has today.
Ditko left Marvel in 1966, but returned in 1979. One of his later creations was Squirrel Girl, who after her debut in 1992 became a cult favorite among comics fans.
He maintained a writing studio in Manhattan until his death, but had no known surviving family members and was incredibly reclusive, turning down nearly all offers to do interviews, meet fans or appear at movie premieres.
“We didn’t approach him,” Scott Derrickson, director of the 2016 movie Doctor Strange, told The Hollywood Reporter.
“He’s like JD Salinger. He is private and has intentionally stayed out of the spotlight. I hope he goes to see the movie wherever he is, because I think we paid homage to his work.”