Anti-Heroes (also spelled Anti Heroes) are heroic characters who lacks several heroic qualities compared to the original heroes of fiction and folklore - these popular characters can be rude, selfish, disloyal, obnoxious, violent, killer or even be a criminal in nature, but will still fight on the side of good, whether they are willing, or forced to. They are not as kind, noble or heroic as their other heroes, but they are ultimately the hero of their stories in spite of their unusual attitudes. Simply put an Anti Hero is a hero with bad qualities who never stops functioning as the hero; he/she saves the day despite having a bad attitude, being a bungler, being selfish, etc. However, they don't have to be selfish, rude, or precisely criminal all the time, they can be polite and nice in nature, due to the part they're not good or evil, but in between the two alignments. One thing almost all anti-heroes have in common, however, is that they live by the philosophy 'the ends justify the means', meaning they employ harsh methods in order to reach their goals.
Examples of popular anti-heroes include Deadpool, Rorschach, Jimmy Hopkins, Dean Winchester, some incarnations of The Doctor from Doctor Who, Ash Williams, Spike from Buffy the Vampire Slayer, Lelouch, Derek Hale, Integra Hellsing, Vegeta, Sasuke Uchiha, Wolverine from the film adaptation of the X-Men comics, Severus Snape, Red X, Shadow the Hedgehog and Diego from Ice Age franchise.