Was it Denny who made the change of Batman and was it only Denny?
Maybe Neal Adams was a big influence. He drew the look of the character and changed day scenes to night scenes before Denny.
There are five people who influenced Denny getting the Batman gig.
Julius Schwartz who became editor of Detective in 1964.
The Camp 1966 TV show which died out in.1968.
Carmine Infantino who became the artist when Julie became editor
1967 Carmine became the Boss DC Editorial Director
Carmine hires Dick Giordano from Charlton, who takes Denny with him to DC.
1968 Denny takes over Justice League from Gardner Fox
Neal Adams was drawing his version of Batman in Brave and Bold Team Ups with Bob Haney before teaming up with Denny.
1971 Comic Book Batman 232 “Daughter of the Demon” writer Denny O’ Neil and atist Neal Adams
Julie did not make major changes in Detrctive. Catmime became artist. Martian Manhunter backup was replaced by Elongated Man a non.serious character. Yellow Circle around Bat Chest Symbol Aunt Harriet Bat signal replaced by phone.
The not all that serious approach convinced Bill Dozier to put the Batman TV show on TV in a ‘camp’ approach.
When.Carmine became Boss as an artist he favored good new artists over old style artists and writers. Wayne Boring was fired from Superman and Gardner Fox and others did not get new assignments.
Part of getting new talent was hiring Giordano who brought along Denny from Charlton.
Denny was formerly a reporter interested in social issues and not come from fandom. He didn’t know who Fox and Finget were or that he was replacing them. He had a wife and baby and did not refuse work though he disliked powerful characters that he was initially assigned to like Justice League and later Superman.
Julie asks Denny to write Batman. Denny says he can’t do Camp.
Fans noticed Neal Adams the ‘good’ Batman artist on Brave and Bold. Carmine would have noticed his talent.
Green Lantern was about to be csnceled. Denny and Neal assigned to work on new Green Lantern Green Arrow emphasing socia iissues. They vecome a team.
Neal was already drawing Batman.
Julie asks Denny the second time to do Batman. Denny agrees and Denny and Neal do their first Batman story together.
So Denny didn’t want to do Canp and wanted to do more realistic characters. The story of Denny looking at the original Batman stories of the late 1930 in the library may not have happened because he was not a fan and unfamiliar with fhe possibility of using the Library. Sometimes he says he did. othertimes not. He had a drinking problem during the time which didn’t help his memories.
Julie gives Denny name of Ra’s with no further detail. He creates the character with Neal devising the Look.
above may partially explain what happened.
Othet factors Denny wanted realism but the Comic Code was also changed in 1971 allowing for horror including vampires. There were several horror titles at the time beginning with Marvel black and white magazines on Dracula.
This helped create an atmosphere for darker chracters.