Sunset Shimmer

Sunset Shimmer is the main antagonist in My Little Pony: Equestria Girls and one of the main protagonists in My Little Pony: Equestria Girls - Rainbow Rocks.

Personality
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 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.

Backstory
Sunset's backstory is explored deeper in the comics. Here, it is shown she had a very troubled relationship with her mentor Princess Celestia, which explains her descent into evil (though she was already extremely arrogant, self-centered, and antisocial, thus her mentor's short patience with her). Sunset had previously appeared in the form of a toy and as a NPC in the MLP Gameloft game. In both versions, she was merely a neutral character and not a truly evil one.

Trivia

 * Sunset Shimmer will become Pooh's enemy but reformed in the end of Pooh's Adventures of My Little Pony: Equestria Girls and will be joining Pooh and his friends the end of Pooh's Adventures of The Harry Hill Movie.
 * Sunset Shimmer will become the FT Squad's enemy but reformed in the end of The FT Squad's Adventures in My Little Pony: Equestria Girls.
 * Sunset Shimmer will become Thomas' enemy but reformed in the end of in Thomas' Adventures of My Little Pony: Equestria Girls and becomes Thomas and Twilight's new friend in Thomas' Adventures of My Little Pony: Equestria Girls - Rainbow Rocks and will be guest starring in Thomas and Twilight Sparkle Visits The Haunted Mansion, Thomas and Twilight Sparkle Spends the Night at the Museum, Thomas and Twilight Sparkle's Adventures of Wallace and Gromit: The Curse of the Were-Rabbit, Thomas and Twilight Sparkle's Adventures of Rock and Rule, Thomas and Twilight Sparkle's Adventures of Disney's Villains' Revenge, Thomas and Twilight Sparkle in Fantasmic (Walt Disney World Version), Thomas and Twilight Sparkle Spends the Night at the Museum 2: Battle of the Smithsonian, Thomas and Twilight Sparkle's Adventures of the Thief and the Cobbler, Thomas and Twilight Sparkle meets George of the Jungle, Thomas and Twilight Sparkle's Adventures of The Prince and the Pauper and Thomas and Twilight Sparkle's Adventures Chronicles helping any friend in need. 
 * Sunset Shimmer will become Brian's enemy but reformed in the end of in Brian Griffin's Adventures of My Little Pony: Equestria Girls.
 * Sunset Shimmer will become G-merl's girlfriend while battling the Dazzlings in Emerl's Adventures Of My Little Pony Equestria Girls: Rainbow Rocks and will be guest starring in Emerl's Adventures Of Power Rangers Megaforce & Super Megaforce.
 * Sunset Shimmer Transformed into an Alicorn in The Night to Remember.
 * Sunset Shimmer along with Twilight Sparkle and Trixie are Princess Yuna's mentors.
 * In Pooh and Brian Griffin's Adventures of Transformers: Age of Extinction, Bowser reveals he made a evil clone of Sunset Shimmer along with a clone Discord and a clone Trixie to get revenge on Twilight and try to kill her.
 * Sunset Shimmer will be Roary and Theodore's enemy but reformed in the end in Roary and Theodore's Adventures of My Little Pony: Equestria Girls and will see them again in Roary and Theodore's Adventures of My Little Pony: Equestria Girls - Rainbow Rocks.
 * Sunset Shimmer will guest star in Brian Griffin and The Hobbit: An Unexpected Journey, Brian Griffin and The Hobbit: The Desolation of Smaug, Brian Griffin and The Hobbit: The Battle of the Five Armies, Brian Griffin's Adventures of The Lord of the Rings: The Fellowship of the Ring, Brian Griffin's Adventures of The Lord of the Rings: The Two Towers, Brian Griffin's Adventures of The Lord of the Rings: The Return of the King and Brian Griffin visits Jurassic World as a reformed character.