Sunset Shimmer

Sunset Shimmer is a former student of Princess Celestia, the main antagonist of My Little Pony: Equestria Girls and protagonist of both My Little Pony Equestria Girls: Rainbow Rocks and My Little Pony Equestria Girls: Friendship Games. She is friends with the Humane 5, Sci-Twi, Twilight Sparkle and Spike (both dragon and dog). She is also one of the Primary protagonists of RCT series.

In My Little Pony: Equestria Girls
Throughout Equestria Girls, Sunset Shimmer is shown to be mean, short-tempered, greedy, bratty, egotistical, cruel, condescending, manipulative, and dishonest. She frequently insults and belittles others, and thinks little of it. According to human Fluttershy, Sunset makes life miserable for "anyone who stands in her way". As a result, much of the Canterlot High student body is afraid of her. She is also shown to be mainly concerned with gaining power, desperately trying various attempts to get Twilight Sparkle's crown in order to use its magic.

However, she doesn't appear to be willing enough to inflict physical pain on others, or at least not upon small animals (i.e. Spike), claiming she isn't a monster. Despite this, she appears to be easily irritated when someone else is praised in her presence, to the point of being provoked into attacking them.

When Sunset puts on the element of magic, she transforms into a demonic visage of herself. While in this form, she becomes more fierce and goes so far as attempting to dispose of Twilight. After she is defeated by the Elements of Harmony, Sunset Shimmer becomes immediately repentant and apologizes for her actions, appearing to renounce her prior dishonest and unkind ways.

In My Litte Pony Eqestria Girls: Rainbow Rocks
In Equestraia Girls - Rainbow Rocks, Sunset Shimmer appears to have completely changed from her old self and started believing in friendship, becoming friends with her former enemies, even Twilight Sparkle, and friendly toward others. She also appears deeply repentant for her actions made at the end of the first film, referring to her altered self as a "raging she-demon". By the end of Rainbow Rocks, Sunset starts writing friendship reports to Princess Twilight using the book she once used to communicate with Princess Celestia.

In My Little Pony Equestria Girls: Friendship Games
In Equestria Girls - Friendship Games, while Sunset has managed to fully integrate herself into the group and able to take mentions of what she did in the past with good humor, she also harbors a fear of losing her school's newly gained trust, and she becomes deeply depressed when she believes she has let them down, despite their assurances. She also becomes increasingly irritated by her struggles to understand how magic works in the human world, briefly snapping at her friends at one point. When the human Twilight Sparkle endangers her friends, Sunset's anger explodes as she berates Twilight for meddling with forces she doesn't understand, taking her own frustrations and self-doubt out on her. However, she immediately regrets her harsh words and reaches out to Twilight in friendship by the end of the film.