It's the most standard, basic aspect of any movie, that the hero has to defeat the villain in order to win the day.
But it's a formula so familiar and so well-worn that, occasionally, filmmakers like to tinker around and present a more challenging, deeply personal obstacle for the protagonist - themselves.
To be clear, we're not just talking about heroes who literally ended their own lives to save the day, but those who had to battle and kill alternate versions of themselves - be it through time travel, cloning or whatnot.
There's probably nothing more paradoxical to the human brain than crossing paths with another iteration of yourself and then having to put them down, but in the case of these 10 movies, that's precisely what the hero had to do in order to win the day.
Whether played for laughs, fan service or serious drama - or maybe even all three - these characters all had to grit their teeth and take their alt-selves out of commission to save themselves, the world, or in one instance, even the universe...