King Mickey Mouse is a pivotal Disney character in the Kingdom Hearts series.
Mickey leaves the castle, tasking Donald and Goofy to find the Keyblade wielder and stick with him. He is not seen again until the very end, where he helps Sora close the door to Kingdom Hearts.
Kingdom Hearts II
Mickey has a much bigger role here, first appearing in Twilight Town after Sora, Donald and Goofy wake up from their one year slumber. He has them meet Yen Sid in his nearby tower, leaving to look into Organization XIII and the origins of its leader Xemnas. Later, he discovers that Xemnas is the Nobody of Xehanort, Ansem the Wise's apprentice. In Radiant Garden, he helps fight off the massive Heartless invasion which is the result of Maleficent's confrontation with Organization XIII.
Mickey returns to Disney Castle after learning that Hades is wreaking havoc there, thwarting his evil plans with the help of Sora, Donald and Goofy.
Mickey Mouse fights with devastating Keyblade combos. He also has possession over all forms of magic that Sora and Donald use, allowing for great triple magic attacks when he is in the party instead of Goofy. Mickey's limit, Twin Keys, allows Sora to wield Mickey's Keyblade to perform devastating twin strikes. The finish, Mouse Mash, has Mickey wield both his Keyblade and Sora's, crossing them for a powerful blast of pure magic which blends Fire, Blizzard and Thunder into one force.