Len Wein, the award-winning writer and editor, perhaps best known for co-creating Swamp Thing for DC Comics and Wolverine for Marvel Comics, along with editing Alan Moore and Dave Gibbons’ Watchmen, passed away Sunday, according to multiple industry reports including word of the news from fellow comics veteran Paul Kupperberg. He was 69 years old.

Wein got his start in comics in 1968 working on DC’s Teen Titans #18. His first Marvel work came in Daredevil #71 in 1970. From there, he continued writing anthology stories for both publishers, along with guest-spots on such titles as Superman and The Flash.

Together with Bernie Wrightson, they created the supernatural superhero Swamp Thing in 1971’s The House of Secrets #92. Swamp Thing would go on to star in various ongoing and miniseries that continue to this day. Wein also contributed to the Man-Thing mythos over at Marvel by introducing the concept of “Whoever Knows Fear Burns at the Man-Thing’s Touch.”

RELATED: Wein’s “Swamp Thing” Homecoming Blurs the Lines Between Man, Monster & Hero

During Wein’s tenure at Marvel, he teamed with artists John Romita Sr. and Herb Trimpe to create Wolverine in The Incredible Hulk #180. In 1975, Wolverine would appear as a member of a revamped X-Men team in Giant-Size X-Men #1, penned by Wein and illustrated by Dave Cockrum. The new lineup that included classic characters like Storm, Nightcrawler, and Colossus would become mainstays across multiple X-Men lineups and volumes.

Wein returned to DC in the late 1970s as a writer and editor, where as the former he created Batman supporting cast member Lucius Fox, and contributed to a rare DC/Marvel crossover in DC Special Series #27. His work as an editor included runs on New Teen Titans, Batman and the Outsiders, and All-Star Squadron, and the aforementioned Watchmen.

Word of Wein’s passing began to spread across social media, with writer Brian Michael Bendis thanking the creator for his work on the X-Men and Swamp Thing. “Len Wein, co-creator of WOLVERINE and SWAMP THING & more responsible for the x-men you love than he gets credit for. Thank you.”

Len Wein, co-creator of WOLVERINE and SWAMP THING & more responsible for the x-men you love than he gets credit for. Thank you. #RIP

— BRIAN MICHAEL BENDIS (@BRIANMBENDIS) September 10, 2017

Tom King posted an image from Batman #15, which shows Commissioner Jim Gordon using Wein’s Marvel nickname.

A shoutout to Len from Batman 15, using his Marvel nickname. Words by me. Art by the @MitchGerads. pic.twitter.com/wSMlGHvh0k

— Tom King (@TomKingTK) September 10, 2017

Legendary creator Neil Gaiman posted a thread of messages to his longtime friend.

I just learned that my friend and writing inspiration @LenWein passed away this morning. My love and condolences to his wife, @mcvalada.

— Neil Gaiman (@neilhimself) September 10, 2017

Len Wein. He wrote Swamp Thing, Phantom Stranger, & my favourite Batman stories. He showed 12 year old me that comics could be literature.

— Neil Gaiman (@neilhimself) September 10, 2017

Len Wein was the editor who brought the British creators to DC. He was one of the nicest people I've met, in 30 years in comics.

— Neil Gaiman (@neilhimself) September 10, 2017

Wein was inducted into the Will Eisner Comic Industry Awards’ Hall of Fame in 2008. CBR sends its condolences to Wein’s friends, family and loved ones at this time.