Biography
Adaptational Sympathy is when a character who either had no motive in the original work or a more twisted motive is explicitly rewritten so audiences might sympathize with them better. If an author is underwhelmed by the motive of a villain in a story with Black-and-White Morality, they might take the opportunity to change it when adapting the work.
Maybe the villain has a brand-new Freudian Excuse in the adaptation. Maybe they're suddenly a Well-Intentioned Extremist who thinks the end justifies any means or a Tragic Villain acting because they have to, not because they want to. They might be Brainwashed and Crazy. Or maybe the world just kept treating them like crap, so they decided they might as well be the bad guy like everyone expects them to. If the hero was a Flat Character, they might get a new backstory to add dynamism. Or, Values Dissonance might come into play if the character's actions in the past would not fly today, so it was changed in order to avoid making it come across as stereotypical.
In Fan Works, this can often overlap with the Draco in Leather Pants treatment, where fans will make a character more sympathetic than they ever were onscreen. Sometimes this will become Ascended Fanon when a Promoted Fanboy gets the chance to work on the franchise.
Compare Adaptational Heroism, which often overlaps, but makes a villain morally sound rather than simply sympathetic. Contrast Adaptational Villainy (where a character is made far less sympathetic at times, though not always), Adaptational Jerkass (where they're a lot meaner than they are in the original work) and Adaptational Nice Guy (where the character is nicer than they were in the original work). To see the Character Development variation of this trope, see Took a Level in Kindness, where a character is made more sympathetic in the franchise itself. See also Perspective Flip and Twice-Told Tale, where this can frequently occur, and Sympathetic P.O.V..
For characters that audiences sympathize with when they aren't supposed to, see Unintentionally Sympathetic. For characters that audiences are supposed to sympathize with, but choose not to do so when their actions come across as otherwise, see Unintentionally Unsympathetic. For characters that audiences feel pity for, see The Woobie for typical examples and Jerkass Woobie for characters with a bit of a mean streak yet still induce pity. For characters that are supposed to be the hero, but audiences see their actions as otherwise, see Designated Hero, or for its opposite, Designated Villain.
No Real Life Examples, Please! This page deals strictly with fictional characters.