The White Witch or simply known as Cassiopeia is the main antagonist of Ni no Kuni who influenced Shadar, caused the death of an untold number of people and is trying to destroy the world so it can be remade into something less flawed.
The White Witch was born as Cassiopeia, daughter of the Wizard King who called her Pea. She was but an infant when he died. They took over ruling Nazcäa and almost completely ran the country into the ground for selfish gains. They allowed a teenager Cassiopeia onto the council as a scapegoat. They'd blame her for all the wrongs.
Cassiopeia only had her parrot Apus as a friend, but she wanted to make the lives of her people better. So she used the forbidden spell Ashes of Resurrection with all the best intentions. The effects though were apocalyptical as all people in Nazcäa turned into monsters and tore each other apart. Cassiopeia was left all alone and waited for someone to come.
She was alone for so long that she began to lose hope. When Pea manifested, as a part of her heart full of innocence, she sent her to Motorville. She then constructed the persona of the White Witch to shield her broken heart. She recreated the Zodiarchs and Apus through her magic in order to escape solitude and became increasingly nihilistic. At some point, she came to believe her world was impure beyond saving and began to plot its destruction and rebirth by her design, creating a world without the potential for the tragedies that made her who she is.
When Lucien finally escaped from imprisonment and torture, she nurtured his power through despair and made him into the Dark Djinn Shadar. He was named by her as Executor of the world.
And she is reprised by Jennifer Bryden in the English dub and Manami Higa in the Japanese dub.