Steve Ditko, the comic-book artist who helped Stan Lee create the Marvel superheroes Spider-Man and Doctor Strange, has died at his home in New York. He was 90.

TMZ reported Friday Ditko was found unresponsive in his apartment June 29 by a social worker who was checking on him.

The Hollywood Reporter said he died two days earlier.

Arteriosclerotic and hypertensive cardiovascular disease were listed as the causes of death, the medical examiner's office 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. Our thoughts are with his family, loved ones, and fans during this sad time," Marvel Entertainment President Dan Buckley said in a statement Saturday.

Marvel Chief Creative Officer Joe Quesada added: "Only a small group of individuals can claim that they have effected and redefined not just an industry, but popular culture worldwide. Steve Ditko was one of those few who dared to break molds every time his pencil and pen hit a blank sheet of paper. In his lifetime he blessed us with gorgeous art, fantastical stories, heroic characters and a mystical persona worthy of some of his greatest creations. And much like his greatest co-creation, Steve Ditko's legend and influence will outlive us all."

"Spider-Man. Dr. Strange. The Question. The Creeper. Shade the Changing Man. Hawk & Dove. He worked with @Marvel AND @DCComics. Such an astounding imagination and the awesome ability to back it up. Thank you #SteveDitko, for sharing your genius and enriching American Pop Culture," tweeted Kevin Smith, filmmaker and former host of AMC's docu-series Comic Book Men.

"RIP to comic book legend Steve Ditko, beyond influential on countless planes of existence. He never truly profited from his comic creations that have lasted for decades, but his work will never be forgotten," Hot Fuzz and Baby Driver director Edgar Wright wrote on Twitter.

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"Goodbye Steve Ditko," said Scott Derrickson, who helmed the 2016 film version of Doctor Strange.

Ditko left Marvel in the late 1960s due to tension with Lee, then worked at the publishers Charlton and DC Comics, returning to Marvel in 1979 to work on Machine Man and the Micronauts. He freelanced for Marvel until the 1990s and one of his final creations was the cult favorite heroine Squirrel Girl.