He is the main antagonist of the "Xehanort Saga", the first part of the Kingdom Hearts series.
In the Pooh's Adventures series, he is an old friend of King Bowser Koopa, having aided Bowser's true father, Morton Koopa Sr., in giving away the young Bowser to the much eviler demon, Dark Specter, for adoption as part of a long term plan to begin creation of the 13 seekers of darkness, who will join together to release Chernabog and the Titans from Tartarus using the power of the X-blade. He is not seen at all in the series.
He is the main villain of the Sora's Adventures Series, goading the young keyblade wielder throughout his adventures by summoning many villains to intercept and capture the boy, such as Winterbolt, Barnaby CrookedMan, Rita Repulsa, and the Disney Villains already under Bowser's employment. Like in the Pooh's Adventures series, Xehanort is not seen at all, preferring to stay behind the scenes while a vessel of his heart, the so-called Ralphscoe, actually a mind-controlled man-child youtube user dragged into the cartoon universe, operates as his front man.