Kaguya Ōtsutsuki

Kaguya Otsutsuki is a legendary figure in the Naruto universe. She was the mother of the Sage of Six Paths and the first human able to use ninjutsu. After Madara Uchiha was assimilated, she took his role, thus becoming the true main antagonist of the series.

History
Over a thousand years ago, Kaguya was a princess who lived during a time of constant strife. In order to end the feud, she consumed the forbidden fruit of the God-Tree. By doing so, she gained godlike powers and was able to stop the wars for the time being. Unfortunately, this also caused the tree to transform into a monster and pursue her in the hopes of reclaiming its power.

It has been said that Kaguya was an extremely domineering woman during her lifetime. Her ability to create jutsu made her a force to be reckoned with and her all-seeing eyes allowed her to watch over humanity. Despite her wishes for a peaceful world, she was not above oppressing free will. This sentiment extended to her sons, whom she resented for sharing her power but not adhering strictly to her oppressive beliefs.

At some point, she became one with the Ten-Tailed Beast, an act that spurred her sons to seal her into the moon. Before she was sealed away, Kaguya conceived Black Zetsu from her thoughts and sent him to hide among the Sage's descendants in the hopes of arranging her revival.

Personality
While she desired to create peace like her sons and grandsons, Kaguya opted for a more forceful method, using her great power to make people submit to her will. As Hagoromo noted, people in time began to fear her as a demon for her methods. Kaguya appears to care very deeply about the earth and didn't want to damage it any further opted to kill Team 7 using natural forces by manipulating the earth. Well-aware of her power, she views the threat of others as insignificant. She appears to be ruthless when compared to Hagoromo as she didn't hesitate to kill Naruto and Sasuke, even though she knew well Hagoromo passed his powers to them and were carrying on his will. She has now came to hate her sons as well.

Despite her desire for peace, Kaguya's knowledge of her own powers and abilities made her develop both a god-complex and messiah-complex, believing chakra rightfully belongs to her alone and that only she can protect and unite the world. She has also been shown to be extremely dangerous, forcing her own sons to seal her away. Kaguya has never forgiven them, openly displaying her hatred towards them and attempting to kill Naruto and Sasuke without remorse, even though they are the reincarnations of her grandchildren and her direct descendants.

Legacy
Kaguya's methods were discarded by her son Hagoromo and his brother in the hopes that a gentler approach would end the wars permanently. Her aggressive methods were passed on by Black Zetsu to her grandson Indra, who would become the progenitor of the war-mongering Uchiha clan. Seeing their potential to reawaken the Rinnegan, Black Zetsu would watch the Uchiha from the shadows for many generations.

Madara Uchiha would later discover the history of ninjutsu and made plans to gain the same power Kaguya had so that he could unite all living things under one illusion.

Kaguya's Return
After succeeding in his task, Black Zetsu turned on Madara and revealed that he was really following Kaguya's will. Black Zetsu then assimilates Madara's body and assumes the form of Kaguya. Kaguya recognizes Naruto and Sasuke as inheritors of her son's powers and deciding that they were the only two who may pose a threat to her vision of a peaceful world, tries to drown them in lava.

Naruto figures out how to levitate and gives Sasuke a platform to float on. Kaguya ambushes the two of them, but instead of killing them, she weeps openly while stroking their faces. As she does so, Black Zetsu materializes on their bodies and reveals Kaguya's history and motivations while siphoning their chakra. Naruto casts off Black Zetsu and exclaims that she's a terrible mother.

Trivia

 * Kaguya is named and based on Princess Kaguya, the main protagonist of the Japanese fairytale The Tale of a Bamboo Cutter, who has been portrayed as a villain in several animes such as Inuyasha & Touhou Project.
 * Her nickname "The Rabbit Goddess" as well as her horns is a reference to popular Japanese folktales of rabbits originating from the moon.
 * The story of Kaguya eating the fruit of the God-Tree is a reference to the biblical story of Eve eating the forbidden fruit.
 * Aside from that, it may also be stated that she is based from Lilith, the first woman who courted with angels & wanted to become a god, metioned in the King James version of the bible.
 * She may be also based from Izanami no Mikoto, the first woman & wife of Izanagi no Mikoto, who later became the goddess of death in Shinto mythology. Like Izanami, both became evil after being betrayed by their loved ones.