Some people don't stop fighting when they're dead. Some actually start fighting after their deaths. These include some characters who are already ghosts, but they continue to fight. They don't "give up the ghost" just yet. They haunt the forces of evil day in and day out. Here are some of the more popular heroic ghosts.
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Deadman
DC Comics' Deadman is a circus performer who is murdered, then given the ability to possess people in order to deliver justice. He represents DC Comics' unique approach to heroes.
The Funky Phantom
As a comic closing to this list, Hanna Barbera brings you the adventures of Jonathan Wellington "Mudsy" Muddlemore, a Revolutionary War soldier who died while hiding in a clock. He is revived as a ghost in the modern day, and the joins a group of teens (much like Scooby Doo's Gang) in solving various crimes that sometimes have a supernatural side to them.
Spectre
Murdered cop Jim Corrigan is sent back as the latest incarnation of the Spectre, a being who visits revenge upon the guilty. He is DC Comics' version of the Furies, with unique and immense powers. In an interesting twist, former Green Lantern Hal Jordan also takes upon the mantle of the Spectre one time.
Black Widow (Claire Voyant)
The original Black Widow of Marvel, Claire Voyant, was a murdered fortune teller who was sent back by the Devil to harvest souls of the wicked. More like an anti-hero than a hero, she still goes after the bad guys and so could be "heroic" in this respect.
Danny Phantom
Danny is the young son of a ghost-hunting couple. An accident with one of their machines transforms him into a ghost-like creature, but with amazing powers. He uses these powers to fight crime in his program that featured on the kids' channel Nickelodeon.
Ghost
What better way to start the list than with someone who's literally named? This Ghost of Dark Horse comics is a white-clad girl named Elisa Cameron who could walk through walls, while toting two 45s. But is she really dead? That's the mystery the series tries to answer.