Banner died after he was shot in the head by an arrow fired by his fellow Marvel Avenger Hawkeye in the new third issue of the Civil War II comic series.
Banner, who has been The Hulk's alter ego since the character's creation in 1962, has been self-medicating in a bid to control his temper tantrums, which bring his monstrous alter ego to life in the series, according to The Hollywood Reporter.
"This is uncharted territory for us. Only two things are for certain: It will take a long, long time for our heroes to come to terms with his loss, and the circumstance surrounding his death will leave a huge scar on the superhero community," Marvel's editor in chief Axel Alonso said.
Banner had recently asked his friend to kill him in the event of any disaster.
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Unlike Captain America and Spider-Man, Marvel bosses have no plans to bring Banner back from the dead.
Ruffalo isn't the only actor who has portrayed Bruce Banner.
Bill Bixby created the character for the late 1970s/early 1980s TV series The Incredible Hulk, while Eric Bana and Edward Norton have played the scientist behind The Hulk on the big screen.