I'm not sure whether you know Rostam or he is a brand new character to you but either way I am absolutely sure that you have never heard the story of this particular wallpaper of Rostam. Some may think that a wallpaper or an image is simply flat and has nothing more than what meets the eyes. While this idea can sometimes be true, it is mostly false about carefully designed images.
Take a look at Rostam wallpaper for instance. At the first glance, it may look like every other game wallpaper. A bulky handsome guy with a massive weapon. Look deeper! Why has it been drawn in this manner? Why do these things exist in the wallpaper? Why has artist chosen these colors?
And Rostam himself, is in a similar situation, people may know him as a hero, the one savior that fights the evil, the typical good guy. but he himself is finding his own place in his world, who he will be, and what he will do. So many don't look into him deeply.
Some are watching him closely, staying in the dark while Rostam is making some crucial decisions, and some of those watchers, want to see Rostam Flourish, some want him as the hero, some want him as the villain.