Mettle fatigue

are no fun. The ancient Greeks, who set the model for Western drama, knew that. Their heroes always come with a fatal flaw, be it psychological or physical. The warrior Achilles is a case in point.

Through the ages, humans have preferred to follow the plight of heroes with a vulnerable side - because that makes them more like us.

It's a moot point whether American heroes such as DC Comics' Superman and Marvel Comics' Spider-Man are the myths of the modern age, although the fanatical devotion of their fans suggests they are more important to their readers than mere pastimes. DC and Marvel, the two major US comic companies, have always offered different versions of heroism. In the 1960s and '70s, DC heroes were generally superhuman, one-dimensional characters, while Marvel's were troubled creatures who pushed their physical limits to a masochistic degree. Marvel's Spider-Man, in "real" life the lovelorn adolescent Peter Parker, is the best known of these.

But one of the most self-absorbed characters is super-rich inventor and arms dealer Tony Stark - also known as Iron Man. Iron Man seems to live in a state of perpetual existential crisis as he flies around in his metallic suit of armour, trying to figure out the morally best course of action. He pushes his body to the point of exhaustion, and has even had an alcohol problem.

Iron Man has, of course, been the star of two hit Hollywood movies, both directed by Jon Favreau. The latest instalment, Iron Man 3, opens in Hong Kong on April 25.

The first Iron Man film won critical acclaim for its portrayal of a superhero with a human side, rather than a vengeful killing machine. Its credibility was helped by the fact that the star, Robert Downey Jnr, had some well-publicised drink and drug troubles in the late '90s.