One of the most important artists of the 20th century in any medium has died. Writer and illustrator Steve Ditko was found dead in his apartment in New York City on June 29, The Hollywood Reporter confirmed. He is believed to have died a few days earlier; no cause of death was given.

Most of the Marvel Comics Universe was created by just a handful of men. Stan Lee, of course, was the writer of many of the comics that shaped modern pop culture, and he famously worked with artist Jack Kirby on books like Fantastic Four and X-Men. Lee’s other crucial collaborator in the early days of Marvel was Ditko, who co-created Marvel’s most beloved character, Spider-Man, after Lee was dissatisfied with Kirby’s initial artwork. The iconic costume that he still wears to this day, both in Marvel Comics and the films, was designed by Ditko.

Working with Lee, Ditko also co-created many of Spider-Man’s most iconic villains, including Green Goblin, Sandman, Vulture, Doctor Octopus, Rhino, the Lizard, Mysterio, and Electro. (You may note that every single villain Spidey has fought in a movie to date with the exception of Venom was a Ditko co-creation.) A few years later, Ditko and Lee co-created Doctor Strange, whose psychedelic adventures in the pages of Strange Tales represent some of the very best comics of their era. The recent Doctor Strange movie, directed by Scott Derrickson, bears a strong resemblance to Ditko’s trippy artwork, particularly in the sequences where Doctor Strange journeys through the multiverse.

Marvel

Ditko left Marvel in the mid-1960s after his creative frustrations with Lee reached a breaking point. As the story goes, the two disagreed strongly about the secret identity of the Green Goblin, and Ditko’s refusal to acquiesce led to his departure. Afterwards, Ditko began writing and illustrating his own stories for a variety of publishers, and his work took on an increasingly philosophical tone. (Ditko was a strong believer in Objectivism and injected its principles into his later work, particularly the crimefighter Mr. A.) At DC, he co-created the Creeper and Hawk and Dove. At Charlton, he worked on books like The Question and Blue Beetle.

It’s also possible some of Ditko’s problems with Lee stemmed from the fact that they were such different people. Lee adored fame and attention; he loved being the gregarious face of Marvel Comics. Ditko, on the other hand, despised the spotlight, and spent the last 40 years avoiding interviews, comic-book conventions, and any kind of publicity. (There are more articles and documentaries about trying to find Ditko than there are articles and documentaries about his actual life.) Biographical details about him are scarce; Wikipedia isn’t even sure if he had a child or not. There’s also some dispute about whether he profited from the Spider-Man movies. In interviews, Ditko insisted he had gotten no money from Marvel or Sony, but a journalist who staked out his apartment a few years ago in an attempt to meet him talked to a neighbor who claimed he’d once seen one of Ditko’s royalty checks.

Regardless, it’s certain that Ditko’s preference for a quiet, anonymous life kept him from receiving the full amount of recognition he deserved. Within hardcore comic fan circles, Ditko is revered as one of the unsung heroes of comics’ Silver Age; among average folks, he’s almost entirely unknown. As a result, a hugely influential comics creator died quietly and with very little fanfare. Which is exactly how he wanted it.