The Sugar Plum Fairy

The Sugar Plum Fairy (also known simply as Sugarplum) is the main antagonist of Disney's 2018 live-action film The Nutcracker and the Four Realms. She is a bitter and devious fairy who seeks to conquer all Four Realms, using Mother Ginger as the pawn in her schemes. She manages to make her intentions hidden until a point where Clara Stahlbaum and Phillip the Nutcracker discover it, at which point they dedicate their efforts in stopping Sugarplum and saving the Four Realms.

Sugarplum is based on the character from the same name from the story by E.T.A. Hoffman and the ballet by Pyotr Ilyich Tchaikovsky.

Background
Many years prior to events of the film, the Sugar Plum Fairy was one of many toys brought to life by a device of the talented inventor Marie Stahlbaum in the Four Realms. She was given domain over the Land of Sweets. The other regents created by Marie to rule over a specific domain included Hawthorne (the ruler of the Land of Flowers), Shiver (the ruler of the Land of Snowflakes) and Mother Ginger (the ruler of the Land of Amusement).

Eventually, Marie decided to leave the Four Realms forever to be with her real human family, leaving the kingdom to be ruled by the other reagents. However, Sugarplum, secretly felt very hurt and betrayed by Marie and decided to get revenge by conquering all the Realms by using Marie's device to create an army of unstoppable tin soldiers. Mother Ginger tried to stop her, but Sugarplum was able to cover her conspiracy by framing the latter, leading to her banishment within her own realm as well as going to war with the other three. During this time Sugarplum searched for the key to activate the device but was unable to find it.

Personality
On the surface, Sugarplum appears childishly innocent and kind, acting very sweet and concerned for the Realms' safety and very adoring of both Marie and Clara, but in reality inside hides a vengeful and embittered mind. After queen Marie left to be with her human family, Sugarplum became resentful of her former queen and became bitter and vindictive, desiring to conquer all the Realms as a sort of childish spite against Marie. Despite this she was able to maintain a kindly facade for years and was manipulative enough to convince the others that Mother Ginger was the evil one and manipulate Clara and Phillip into getting the key for her.

Sugarplum is very ruthless and doesn't care who she hurts to get what she wanted. This was fist shown when she used Tin Soldiers, which were described by Phillip as "hallow" and casually transformed one of her own (sentient) loyal soldiers back into a toy just to demonstrate what she planned to do to the other leaders once she had taken over.

Despite all her evil, at her core she is essentially a hurt and angry child whose entire actions mirror a child lashing out at their parents for their supposed abandonment. So much that she goes as far as to destroy all her "mothers" creations and even her own "siblings" without any shame or conscious, yet still retaining an intelligence and patience necessary to manipulate events to her choosing. She also appears to be very vain, boasting about how prettier she is than Mother Ginger.

Beginnings
The Sugar Plum Fairy started off as a lifeless porcelain doll owned by Marie Stahlbaum when she was a child, but was brought to life after Marie created the Four Realms as its first Queen. Sugarplum was assigned by Marie to rule over the Land of Sweets while three other regents (Mother Ginger, Shivers and Hawthorne) were assigned to rule the remaining realms.

At first, Sugarplum felt comfortable being in the service of Marie, but as the years went by, Marie decided to leave the Four Realms for her family, so she left the four regents in complete charge of the Four Realms. Though Ginger, Hawthrone and Shivers accepted this new change in leadership, Sugarplum secretly disapproved this as she felt betrayed and abandoned by Marie. She then decided that it was time to take over the Four Realms as its new Queen and rebuild them in her own image to alleviate her pain.

Sugarplum soon learned that Marie created a machine capable of converting toys into living objects (presumably the same one that brought her to life), and formulated a plot to create and bring life to an army of Tin Soldiers to accomplish her goal. However, Ginger learned of Sugarplum's plot and tried to stop her, only to be framed by the latter for trying to incite the plot, resulting Ginger's banishment within her own realm and a war against the other three realms. Despite the setback, Sugarplum is distraught to learn that a certain key that can activate the machine is lost within the Realms, forcing herself to maintain her cover.

Meeting Clara
During one Christmas Eve, an ill Marie gets her husband to give their children Christmas presents as her dying wish. Her youngest daughter Clara receives a handcrafted egg-shaped box, and is told by her godfather Drosselmeyer that Marie created it for her. After getting into an argument with her father at the ballroom for refusing to dance with him, Clara finds a string signifying her gift, which leads her into the Four Realms. There, Clara spots the key hanging on a tree, but a mouse steals it for Ginger, much to her dismay.

Clara approaches Captain Philip Hoffman, who takes her over to see Sugarplum, Hawthorne and Shivers, who are all delighted to see the daughter of their former queen. Sugarplum explains to Clara about the history of the Four Realm and the machine, in which she and the other regents intending to use it to defend their realms against Ginger and her forces. Sugarplum then sends over Hoffman and several soldiers to aid Clara in confronting Ginger and successfully stealing back the key, but Clara is annoyed to find out that the egg turns out to be a music box after being locked by the key.

True Colors
With the key finally in her possession, Sugarplum uses the machine to bring the Tin Soldiers to life, revealing her true colors by admitting that she felt resentful towards Marie for leaving the Realms and that she intends to use her army to take over the Realms as its new Queen. She also informs that the machine can also revert any person living in the Realm back into a toy and that she plans to use it on those who would defy her new reign. With everything in her control, Sugarplum imprisons Clara, Hoffman and the other regents before heading out to initiate her invasion on the Realms.

However, Clara and the others escape while Hoffman convinces Ginger and her minions to help them foil Sugarplum's plot. As Sugarplum directs her Tin Soldier army to invade the Land of Amusements, Hoffman and Ginger's minions fight against several of the Tin Soldiers. In the meantime, Clara enters the machine's room and shuts it down, causing the palace's water wheels to cease rotating and catching Sugarplum's attention.

Death
As Mother Ginger fights off several Tin Soldiers to buy Clara more time, an angry Sugarplum summons more Tin Soldiers to trap both of them. Ginger and Clara tried to reason with Sugarplum by admitting that they understood how she felt about Marie's departure, but Sugarplum refused to listen as she intends to turn Ginger into a toy with the machine. However, Clara revealed that she already reprogrammed the machine into zapping Sugarplum, who is turned back into a lifeless porcelain doll as punishment for her crimes. With Sugarplum's magic undone, all the Tin Soldiers became lifeless as well, thus ending Sugarplum's reign of terror for good.

Trivia

 * In both the original story and the ballet, she was a heroic figure, while the Mouse King was the main villain. On the Disney adaptation, their roles are switched instead.
 * She speaks with a French accent and uses the occasional French word.