The comics writer and editor who co-created DC Comics’ Swamp Thing, Len Wein, has died, according to multiple reports.

In an interview with the Comics Bulletin in 2003, Wein recalled that he started reading comics during a hospital stay when he was 7 years old. As a teenager, he and pal Marv Wolfman would take weekly tours of the DC Comics offices. Both Wein and Wolfman were hired as freelance writers in the 1960s, kicking off a prolific career as both a writer and an editor.

Wein is credited as the creator or co-creator of a number of fan favorite characters, including Wolverine, Storm, Colossus, Swamp Thing, Lucius Fox and Human Target. In 1974, he was named editor-in-chief at Marvel Comics. His run lasted a year before he was succeeded by Wolfman. He stayed on as a writer, with heralded runs on comics including Thor, The Incredible Hulk and Fantastic Four, among others.

As a writer for DC Comics, he had runs on Batman and Green Lantern. As an editor, Wein worked on Watchmen with Alan Moore and Dave Gibbons, as well as Batman and the Outsiders and the New Teen Titans.

Wein, who underwent quintuple bypass heart surgery in February 2015, had recently expressed on Twitter that he was dealing with some health issues. Comics professionals who worked with him and who were inspired by him have eulogized their friend and colleague on Twitter (some selected tweets have been posted here).