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.
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.
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.
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.