Best known as co-creator of the iconic superhero Spider-Man, as well as for his reclusive withdrawal from comic book fandom and acclaim, Steve Ditko, one of Marvel’s most celebrated comics artists, was found dead in his Manhattan apartment June 29. He was 90.

Along with artist Jack Kirby and publisher/impresario Stan Lee, Ditko is considered one of the most influential comic book artists to come out of Marvel during the early and middle 1960s, a seminal period in the history of Marvel and of the American superhero genre. Along with Lee and Kirby, Ditko is credited with co-creating Spider-Man, a revolutionary superhero at the time, a character that has gone on to become as iconic and as commercially profitable as Superman or Batman, both published by Marvel’s longtime rival publisher, DC Comics. Although Kirby was first assigned the job of designing the character, it was Ditko’s version (both the character design and narrative portrayal) that best captured the qualities that Lee outlined when the series was first published in 1962.

Unlike earlier teen superheroes, who were usually the sidekick to other heroes, Spider-Man, along his alter ego, teenage prodigy and news photographer Peter Parker, was something different for a new generation of comics fans. Wracked by teenage problems of isolation, insecurity and social rejection, Parker lived at home in Queens, New York with his aunt May, and seemed to always be scraping to make money.

Ditko’s artwork was particularly striking and unusual for the time. His drawings seemed overcast with psychological gloom and his drawings imbued New York City, where Marvel comics heroes were set, with an appropriately gritty, dark and moody urban sensibility. Ditko’s drawings of Spider-Man’s high-flying antics were dynamically rendered—Spidey’s bodily actions were anatomically precise as well as kinetic--and his fight scenes were meticulously choreographed and so cinematically rendered, the characters seemed to move right across the page.

Although celebrated for his work on Spider-Man, Ditko produced an extraordinary body of work over a very long career in comics that began in the early 1950s. In addition to Spider-Man, Ditko created Dr. Strange, a master of the supernatural arts, a classic and popular Marvel character that was first published in 1963. But Ditko’s work spanned every genre and he worked for most of the publishers of the Silver Age of Comics (1950s-1970), and his work included horror, science fiction, mystery and crime. Over his career he worked for such defunct publishers as Charlton, as well as for Marvel and DC. At DC, he created such superhero series as Shade, the Changing Man, The Question and The Creeper and later worked on indie comics at Pacific Comics, Eclipse, and Dark Horse.

Despite Ditko’s popularity among both fans and comics critics, he was a reclusive and inscrutable figure. He has long been associated with Ayn Rand’s libertarian-like philosophy of Objectivism, which is credited as being the basis for Ditko’s creation of Mr. A, a severe character dressed in suit and fedora and published in black and white that is driven by an equally hard-edge philosophy of absolute right, absolute wrong and absolute moral judgement. Ditko’s career was also marked by an endless series of disagreements with editors and publishers—most famously his dispute with Stan Lee—some over money and credit; others somewhat mysterious. These disputes usually resulted in his refusal to continue to work with them.

Although considered friendly and approachable when encountered, Ditko nevertheless declined most recorded interviews and photographs, and remained a mysterious, albeit iconic and revered, figure living in the same apartment in midtown Manhattan for decades.