A hero alone,
is front of a background hinting danger or entrapment. Our heroes and heroines stand alone against adversaries you’re well aware of.
To reach “hero” status,
requires a character we’re very familiar with their back story. They have either already overcome challenges or continuing to. Otherwise, we just see an actor standing in front of a Photoshopped blue screen. The assumed knowledge of history is the power of the poster. We know everything about them and they convey a message just standing there.
What’s the point?
We’re seeing the character as opposed as the talent in many other posters. The poster is more effective if we the audience feel a connection with the subject. The background is usually drab with a flare of excitement or danger. It doesn’t distract yet invites our imagination what the hero will do. It is basic Hollywood formula popular with U.S. audiences, one against the world.
Most recent example, The Hobbit: Battle of the Five Armies
Bilbo Baggins, tired and fatigued after the first two films, stands or kneels alone. What must he do to make it to the end? Will he make it? Of course, after watching the first 2 or 5 films, we know who he is and what his journey is about. The background is ambiguous and doesn’t contribute anything definite. But it does place him in our visions of Middle Earth and we are drawn into the film to find out more.