Master Xehanort is the main antagonist of the Dark Seeker Saga in the Kingdom Hearts franchise and one of the deuteragonist of the prequel,Union X Cross. He is the original incarnation of Xehanort from which Ansem, Seeker of Darkness, Xemnas and all others spawned. He manipulated almost every event in the series, and devised many backup plans that involve dividing his heart among 13 different beings created from his power and take over the universe. He is the archenemy of the Guardians of Light.
Master Xehanort was a Keyblade Master, the first master of Ventus, and the creator and master of Vanitas, the original incarnation of Ansem and Xemnas and the future self of Young Xehanort. He served as the main antagonist of both Kingdom Hearts: Birth by Sleep and Kingdom Hearts III and the overarching antagonist of Kingdom Hearts 3D: Dream Drop Distance, being the true villain who has orchestrated the whole event.