However, comics historian Les Daniels considers O'Neil's "vengeful obsessive-compulsive" Batman to be an original interpretation that has influenced all subsequent portrayals of the character.

His other notable work includes creating Richard Dragon with Jim Berry, and runs on The Shadow with Michael Kaluta and The Question with Denys Cowan.

[1] O'Neil graduated from Saint Louis University around the turn of the 1960s with a degree centered on English literature, creative writing, and philosophy.

O'Neil wrote bi-weekly columns for the youth page, and during the slow summer months he filled the space with a series on the revival of the comics industry.

[12] Briefly returning to Marvel a few years later, O'Neil and artist Neal Adams revived the Professor X character in X-Men #65[13] in one of the creative team's earliest collaborations.

In 1968, Dick Giordano was offered an editorial position at DC Comics and took a number of Charlton freelancers with him, including O'Neil.

With artist Mike Sekowsky, he took away Wonder Woman's powers,[18] exiled her from the Amazon community, and set her off, uncostumed, into international intrigues with her blind mentor, I Ching.

These changes did not sit well with Wonder Woman's older fans, particularly feminists, and O'Neil later acknowledged that de-powering DC's most well-known superheroine had unintentionally alienated readers.

[19] In Justice League, he had more success, scripting socially and politically themed stories that presaged his later work on Green Lantern/Green Arrow.

[1] He and artist Dick Dillin made several changes to the membership of the JLA by removing founding members the Martian Manhunter and Wonder Woman.

[20] Following the lead set by Bob Haney and Neal Adams in a Brave and the Bold story that visually redefined Green Arrow into the version that appeared in comics between 1969 and 1986, O'Neil stripped him of his wealth and playboy status, making him an urban hero.

[24] O'Neil's 1970s run on the Batman titles, under the direction of editor Julius Schwartz,[25] is perhaps his best-known endeavor, getting back to the character's darker roots after a period dominated by the campiness of the 1960s TV series.

[26] Comics historian Les Daniels observed that "O'Neil's interpretation of Batman as a vengeful obsessive-compulsive, which he modestly describes as a return to the roots, was actually an act of creative imagination that has influenced every subsequent version of the Dark Knight.

"[27] O'Neil and Adams' creation Ra's al Ghul was introduced in the story "Daughter of the Demon" in Batman #232 (June 1971).

[29] During this period, O'Neil frequently teamed up with Adams (with Giordano often assisting on inks) on a number of memorable issues of both Batman and Detective Comics.

in Batman #251 (Sept. 1973), a landmark story bringing the character back to his roots as a homicidal maniac who murders people on a whim and delights in his mayhem.

[31][32] O'Neil and Giordano created the Batman supporting character Leslie Thompkins in the story "There Is No Hope in Crime Alley" in Detective Comics #457 (March 1976).

[37] Later that same year, O'Neil and artist Michael Kaluta produced an "atmospheric interpretation" of the 1930s pulp hero in The Shadow series.

[11] While working for Marvel, he helped write the original character concept for The Transformers, and is credited as the person who named Optimus Prime.

[50] Between the years of 1988 and 1990, O'Neil would return to Green Arrow by writing the Annuals, while Mike Grell wrote the monthly title.

The Batman: Legends of the Dark Knight series began in 1989 with the five-part "Shaman" storyline by O'Neil and artist Ed Hannigan.

In the opening of the novelization, O'Neil stated that part of the reason "Knightfall" was written was due to the recent popularity of more "ruthless" heroes such as the Terminator and James Bond in films, as editors were starting to wonder if readers would prefer a Batman who was willing to kill his opponents.

[57] After the conclusion of Knightfall, O'Neil wrote the 100-issue Azrael comic series, chronicling Valley's battles against the Order of St. Dumas, between 1995 and 2003.

O'Neil modeled the series on Arthurian legends, comparing Azrael's quest to discover the truth about himself to the Holy Grail.

[1] He fired writer Roger McKenzie so that Miller could both write and pencil Daredevil, a decision which then-Marvel editor-in-chief Jim Shooter says saved the series from cancellation.

He shared a 1971 Goethe Award with artist Neal Adams for "Favorite Comic-Book Story" for "No Evil Shall Escape My Sight.

The Perfesser is depicted as a tall, pipe-smoking genius who often gets lost in his own thoughts; his name is likely derived from Cosmo "Perfessor" Fishhawk of Shoe, which O'Neil was a known reader of.