I'm still talking about heroes and the different kinds of them. In today's market, the dark hero or anti-hero is very popular. If you want to get technical, according to most of the writing books I have, an "anti-hero" is someone who would usually be a villain in the role of protagonist. That would be something like a story about a pirate in which we're encouraged to cheer for him evading the Royal Navy, a bank robber in which we're hoping he'll elude the police, mobster stories, heist and caper stories, etc. But people often use the term anti-hero to describe a hero who does things that aren't generally considered "heroic" -- the hero who's more violent than he should be, who breaks the law or bends the rules in the name of the greater good. I'd generally consider that a "dark" hero, but the lines get blurry, and some characters cross over the lines, so I'll discuss both in the same post.
If we're going by the technical definition, I think the main dividing line between a dark hero and an anti-hero would be whether the hero is doing what he's doing for the greater good. A dark hero might be doing illegal things, but he's doing so because they're necessary for a cause outside himself. Or he might be breaking the law of an unjust government. Robin Hood might be an example. He's a thief, but he's targeting the corrupt and redirecting their wealth to the needy. An anti-hero would be stealing for his own gain. An example of that might be the con-man hero of the movie Catch Me If You Can, who until the end of the movie is using his considerable skills to move himself up in the world and make his own life more luxurious and exciting.
But a character can sometimes be both. One good example might be Mal Reynolds from the TV series Firefly. He was a thief, scavenger and smuggler. In some episodes, he and his crew were openly pulling criminal heists. Their usual victims were the corrupt government or corrupt individuals, but the profits from these jobs went to the crew, not to any kind of aid to poor people. But then Mal was also a sucker for an underdog and had a habit of taking "jobs" for no real pay in order to help someone who needed help. He was on the wrong side of the law, but only sometimes was he a true anti-hero.
Then there are the pseudo anti-heroes, the characters where their illegal background is more about character development than plot -- the bad boys with hearts of gold. There's Han Solo in the Star Wars movies, who was a smuggler before his entry into the story. We see the consequences of his criminal background, but once he's in the story, he doesn't really do anything criminal. A similar example would be Duke Crocker on the TV series Haven. He's a criminal and smuggler, and there are references to his criminal activity throughout the series, but he isn't really an anti-hero because his role in the story isn't about his criminal life -- it's not about him pulling off a job that we hope he gets away with. His criminal life is character development and a source of conflict when circumstances force him to team up with his childhood friend, who's now a cop, in order to save the town.
A dark hero might be someone who behaves like a villain, even as he works toward the greater good. He might be violent, he might not care about collateral damage, he might be a generally nasty person, but he's putting himself on the line against evil. Urban fantasy is full of this kind of figure.
Dark heroes and anti-heroes are really popular right now, and there don't seem to be a lot of limits as to how dark you can go. If someone can pull off a serial killer as a hero, you've got a lot of room to work with. But you still have to make the audience identify with and believe in these characters. They have to be human beings. Show a variety of their relationships. Give them people they care about, and who care about them. If someone we like loves these people, we can see that they're lovable. Or maybe they've lost someone they loved, and we see their pain over that.
Give them motivation or some explanation for why they're the way they are. Going back to Catch Me if You Can, we saw the way that young man was brought up and how unhappy his life became when everything fell apart, so we understood his need to escape into a fantasy world, even if that world was created with illegal acts. The bank robber doesn't necessarily have to be getting money for his mother's lifesaving operation, but we need to see why he's willing to go to these lengths to get money. Mal Reynolds in Firefly was desperately trying to maintain his independence by having his own ship and his own crew, and he would do anything to keep his ship running and to provide for his crew.
You can also gain audience sympathy by making a character like this charming and highly skilled. We like caper stories because they bring together a team of people with specialized abilities who are usually the best at what they do. It's fascinating watching them work, even if we don't sympathize with what they're doing.
These days, it may actually be more difficult to make audiences love a truly good hero than a dark hero. There are ways to do it, though, and I'll talk about that next time.