“He wrote or edited almost every major DC character — there’s hardly a facet of DC’s world that Len didn’t touch,” Diane Nelson, the president of DC Entertainment, said Sunday in a statement.

“Len was the nerd’s nerd,” Tom King, the Washington-based comics writer for Marvel and DC, told The Washington Post’s Comic Riffs. “He was a fanboy of the generation of writers that [preceded] him, a leader and innovator of his own generation of writers, and an inspiration to the generations of writers that followed him.

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“And he was just a nice guy who took pride in a medium that many wrongly dismissed.”

Mr. Wein, who broke into the comic-book industry five decades ago, while barely more than a teenager, died in the Los Angeles area, DC Comics announced Sunday. The cause of death has not been reported following his extended hospital stay in recent weeks, according to multiple sources. He was 69.

Mr. Wein, who was born in New York on June 12, 1948, grew up as a self-described “sickly” child, and it was during a hospitalization as a kid that he began to read comics.

“His connection to DC Comics goes back to the early 1960s, when he and his friend [and future collaborator] Marv Wolfman would take a tour of the DC offices that was offered once a week,” according to the publisher.

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The pair created fanzines, then sold their first scripts to DC in 1968. His first professional work was on that year’s “Teen Titans,” through which he and Wolfman introduced Starfire/Red Star. Two years later, he produced his first Marvel work, for “Daredevil” with Roy Thomas.

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“Marvel was lucky to have Len Wein as a writer,” legendary Marvel editor Stan Lee told The Post, “because he was talented, enthusiastic and always did nothing less than his very best.”

In 1971, Wein co-created the Swamp Thing (“The House of Secrets No. 92”) with Bernie Wrightson, who died earlier this year.

Three years later, Mr. Wein, working with artists John Romita Sr. and Herb Trimpe, created Wolverine for “The Incredible Hulk No. 180,” and the character, as drawn by Dave Cockrum, would appear in the updated team-up “Giant-Size X-Men No. 1,” which also features Storm and Nightcrawler.

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Hugh Jackman, who has portrayed Wolverine on screen for nearly two decades, said Sunday that he first met Wein in 2008, tweeting: “From his heart, mind & hands came the greatest character in comics.”

Mr. Wein, who edited Alan Moore and Dave Gibbons’s mid-’80s epic “Watchmen,” was hailed by such creators as Neil Gaiman as the guiding force behind DC’s “British invasion” of talent.

He was inducted into the Will Eisner Hall of Fame in 2008.

He is survived by his wife, Christine Valada, and children.

Here is some of the social-media outpouring from industry pros: