Starlight Glimmer was formally introduced in Season 5's two-part premiere "The Cutie Map", where she was set up to be Season 5's main antagonist. She was the leader of a small town located in a desert-like area. Starlight had actually brainwashed the town's citizens into believing her false sense of equality by taking away one's cutie marks to live a happy life, which she did to Twilight Sparkle and her friends. However, they find out that Starlight still holds on to her cutie mark, turning the townspeople against her for lying to them. Despite being outnumbered, she was able t flee from her situation, and spent the remainder of the season spying on Twilight Sparkle and her friends.
Starlight returned in the two-part finale "The Cutie Re-Mark" to get her revenge on Twilight Sparkle for turning her cult against her. Starlight and Twilight constantly fought each other in various timelines that Starlight kept trying to alter. Every time Starlight altered space and time, it made Twilight's past threat the biggest threat/new ruler of Equestria in each timeline. When it escalated into having Equestria turned into a barren and stormy wasteland, Twilight convinces Starlight to show her why she was acting this way. Starlight revealed that she once had a friend named Sunburst, who had fun and solved problems with her when she was a filly. However, when Sunburst received his Cutie Mark, he left town, leaving Starlight alone and sad. This caused her to resent cutie marks immensely, but despite this, Twilight forgives Starlight and did not impose charges on her if she agreed to be her student to amend her past wrongdoings.
Starlight Glimmer returns once more in Season 6, where she gets a new hairstyle, signifying her change of character. She went to the Crystal Empire with Twilight to try to reunite with Sunburst, who now lives there. Spike went along with Starlight to ensure that she does what Twilight told her to. After a series of awkward conversations with Sunburst, Starlight finally manages to convince her old friend to fix the Crystal Empire's recently destroyed power source to get rid of an incoming storm. Starlight was able to reconcile with Sunburst, who decided to remain behind in order to look after Flurry Heart, the newborn daughter of Princess Cadence.
Starlight would then currently spend the entirety of Season 6 learning a lot about friendship under Twilight Sparkle's supervision. She was even able to befriend Trixie, despite Twilight's distrust towards her.
Starlight Glimmer has received somewhat mixed reception as a villain. Some people are put off from her petty attitude, even in her debut, which was not helped by her excuse for enslaving an entire town in the season finale.
Despite her polarizing status as a villain, some people actually appreciate her for being the first villain of the show to actually survive an entire season from start to finish.
While some people prefer Sunset Shimmer for having a similar, but better redemption arc, others are willing to enjoy Starlight for being a recurring character of importance for Season 6.
Since she has a lot of cute moments throughout Seasons 5 and 6, she has earned the nickname "Glim Glam" by some.
Her relationship with Sunburst was even praised by many, which was helped considerably in Season 6's two-part premiere.