Acclaimed comic book writer Dennis "Denny" O'Neil has passed away at the age of 81.

As reported by Newsarama, O'Neil's family says he died in his home on June 11 of natural causes.

O'Neil was born in 1939 in St. Louis, MO, and after graduating from college, he joined the Navy before eventually landing a job writing columns for a newspaper. This put him on the radar of Roy Thomas, who helped him get his start at Marvel, where he wrote Strange Tales, Rawhide Kid, Millie the Model, Daredevil, X-Men and more.

After his initial stint at Marvel, O'Neil worked with Dick Giordano at Charlton Comics under the pseudonym Sergius O'Shaugnessy and in 1968, Giordano brought him over to DC, where he shook up the status quo on Wonder Woman and Justice League of America and introduced The Creeper. The JLA run, in particular, helped lay the foundation for one of O'Neil's most notable works, Green Lantern/Green Arrow, as well as the story in Green Lantern #85-86 in which Roy Harper/Speedy was revealed to be addicted to heroin.

O'Neil is also credited with bringing Batman back to his gritty roots in the 1970s following the fan-favorite 1960s television series starring Adam West. During this time, he co-created the iconic Batman foe Ra's al Ghul, helped revitalize Two-Face and The Joker, co-created Leslie Thompkins and killed off the original incarnation of Batwoman, Kathy Kane.

Other notable titles O'Neil worked on include Superman, Superman vs. Muhammad Ali, The Shadow, Captain Marvel, The Question, The Amazing Spider-Man and novelizations of Batman Begins and The Dark Knight, and he's credited as the co-creator of Madame Web, Hydro-Man, Obadiah stane/Iron Monger, the Silver Centurian armor, Yuriko Oyama (the future Lady Deathstrike), Azrael and many more.

Outside of writing, O'Neil served on the editorial staff at both Marvel and DC, as well as the board of directors for The Hero Initiative.