Queen of a swarm of an insect-like race called Changelings, Chrysalis acts as their undisputed leader. As their single authority figure, she is also determined to feed her loyal subjects, at any cost. Gifted with her natural ability to change her appearance, a talent all Changelings share, she once personally lead an espionage mission into the heart of Equestria's capital city of Canterlot... With the goal to swarm all over Equestria, once the royal hiearchy is disarmed and left defenseless.
Originally never referred to as "Queen Chrysalis" in her cartoon appearances, outside of the Swedish dubbed version of the show, where Princess Celestia directly refers to her by name. Despite this, she was given the name anyways, as it was listed in the show's script. Designed to be a gangly black "pegacorn" (the term now updated to "Alicorn", a creature having both properties of a unicorn and pegasus), she influenced the rest of the Changelings character designs, from the inspiration of her name being decided as "Chrysalis".
Being a "Changeling", her race references a similar mythological creature. In the myth, Changelings were suspected to steal babies and replace them with impostors, who feeds off their parents love for them. Similarly, Chrysalis and her minions also feed off of the love and affection of their prey, disguising themselves to feed off of the love meant for others.
Very little history is known about her, besides multiple references to her dream to seize a food source as big as Equestria since she was small. Also recalling swarming over many lands with her swarm, no doubt ravaging them before departing, she claims that Equestria has more love than any place she's ever encountered.
In her most recent appearances in the comics from IDW Publishing, she's resurfaced after her defeat in Canterlot. Targeting Ponyville to be her next Changeling stronghold, she quickly begins to hunt ponies down and capture them, replacing them with Changelings. Twilight Sparkle quickly deduces that Ponyville's zombie-like inhabitence must've been swarmed by Changelings. Tracking them down into town hall, Twilight and her friends find where Ponyville's citizens were being held captive, in Changeling chrysalises.
After fighting off a swarm of Changelings on guard, Twilight and her friends break the hostages from their organic prisons. Spike then coughes out an ominous crystal ball type display, his fire breath delivering it through teleportation. Queen Chrysalis appears in the orb, where she reveals she has three more hostages in her Kingdom, the Cutie Mark Crusaders. Giving Twilight and her friend three days to rescue them, Chrysalis's message then fades out, Scootaloo inadvertently stopping her before she elaborates on her master plan. Naturally, the mane six all suspect it to be some sort of trap. Nevertheless, Applejack and Rarity are determined to take their chances anyways, as their sisters are part of the CMC.