Sugar Plum Fairy

Sugar Plum Fairy (also known simply as Sugarplum) is the hidden 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.

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.