In ancient literature, heroes were usually described as males who sacrificed themselves for the benefit of others. They also held certain characteristic such as can be seen through the chivalric code. They were expected to do great deeds of glory to even be counted as a hero in their society. This is why literature such as King Arthur were so popular in their times.
Although heroism in modern can still be represented through the lens of a superhero or war hero, it is generally given a lot more lax, and usually a lot easier to obtain. Unlike in the times of the knights, most people aren't expected to slay dragons, or rescue a damsel in distress. The theme of the "everyday hero" is certainly a huge difference between the two. In modern film, heroes are usually portrayed as the average Joe, sort of character, with flaws and vices just like anyone else. Heroes are now seen as obtainable characters with decent stances of virtue.
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The theme of The Count of Monte Cristo is revenge and forgiveness, power and powerlessness. When Dantes is given a life-prison sentence by his enemies, he spends every waking moment planning his revenge
