Because you like Sophie Sheridan in Mamma Mia!
Stuck somewhere between life and death, Talion is motivated by one thing only: vengeance. See them in Middle-earth: Shadow of Mordor.
The only thing Albert Wesker cares about is turning himself into a God. See them in Resident Evil Series.
Big Boss is a disillusioned mercenary commander who wants to create a world for soldiers (and soldiers alone). See them in Metal Gear Series.
It's hard enough fighting a war. But it's worse for Commander Shepard, knowing no matter how hard you try, you can't save them all. See them in Mass Effect.
Pro: Johan Liebert is handsome and charming. Con: he's also a sociopathic killer. See them in Monster (TV Show).
A fight every now and then makes Dante's life a little more interesting. See them in Devil May Cry.