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 make her guest starring appearance in Pooh's Adventures of Jupiter Ascending, Pooh's Adventures of Titan A.E. and Pooh's Adventures of Planet Dinosaur
 * 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 Pirates of the Caribbean: On Stranger Tides, Thomas, Twilight Sparkle and the Adventures of Rocky and Bullwinke, Thomas the Tank Engine meets the Hunchback of Notre Dame, Thomas and Twilight Sparkle's Adventures of Osmosis Jones, 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's Adventures of the Thief and the Cobbler, 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 Tom and Jerry: The Movie, Thomas and Twilight Sparkle meets George of the Jungle, Thomas and Twilight Sparkle's Adventures of The Prince and the Pauper, Thomas and Twilight Sparkle's Adventures of Looney Tunes: Back in Action, Thomas and Twilight Sparkle's Adventures of Cloudy with a Chance of Meatballs, Thomas and Twilight Sparkle's Adventures of Cloudy with a Chance of Meatballs 2, Thomas and Twilight Sparkle's Adventures of Disneyland Fun, Thomas and Twilight Sparkle's Adventures of Epic Mickey  and Thomas and Twilight Sparkle's Adventures Chronicles. 
 * Sunset Shimmer will become Ash Ketchum's enemy, but reformed in Ash's Adventures of My Little Pony: Equestria Girls and will meet Ash and his friends again in Ash's Adventures of My Little Pony: Equestria Girls - Rainbow Rocks and will be guest starring in Ash Ketchum meets Spirit: Stallion of the Cimarron
 * Sunset Shimmer will become Brian Griffin's enemy in Brian Griffin's Adventures of My Little Pony: Equestria Girls, but will reform, and will meet him again in Brian Griffin's Adventures of My Little Pony: Equestria Girls - Rainbow Rocks and she'll guest star in Brian Griffin meets Astro Boy, Brian Griffin's Adventures of Fantastic Mr. Fox, Brian Griffin's Adventures of Batman: Mask of the Phantasm, Brian Griffin enters The Polar Express, Brian Griffin's Adventures of National Lampoon's Vacation, 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, Brian Griffin's Adventures of National Lampoon's Christmas Vacation, Brian Griffin's Adventures of Batman: Under the Red Hood, Brian Griffin's Adventures of Star Wars Episode VII: The Force Awakens, Brian Griffin's Adventures of Star Wars Episode VIII, Brian Griffin's Adventures of Star Wars Episode IX, Brian Griffin's Adventures of Star Trek, Brian Griffin's Adventures of Star Trek: Into Darkness, Brian Griffin visits Jurassic World, Brian Griffin's Adventures of Power Rangers: S.P.D., Brian Griffin goes Walking with Monsters: Life Before Dinosaurs, Brian Griffin goes Walking with Dinosaurs, Brian Griffin goes Walking with Prehistoric Beast and Brian Griffin's Adventures Chronicles.
 * 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.
 * 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 Winnie the Pooh Saves Captain Phillips.