Merlin

Merlin is a sorcerer that first appeared in Kingdom Hearts. He helps Sora understand magic when the boy appeared in Traverse Town.

Kingdom Hearts
''A great sorcerer living on the outskirts of Traverse Town. Merlin's wisdom and magic powers rank second to none, and he teaches Sora and his friends about magic. He has a mysterious bag that can hold anything, no matter how large. Merlin first tutored Arthur in how to be king in "The Sword in the Stone" (1963).''

Kingdom Hearts II
''A powerful wizard who's currently living in Hollow Bastion. He's letting the Hollow Bastion Restoration Committee use his house as a meeting place.''

''Merlin has wisdom and magical powers that are second to none, and he taught Donald most of what he knows about magic. He also has a mysterious bag that can hold anything, no matter how big it is.''

Kingdom Hearts
Merlin is first introduced as a resident of Traverse Town, and one of the survivors from Hollow Bastion. He lives in a ramshackled house hidden in a secret underground lake behind a wooden door with a fire symbol, located in the Third District of Traverse Town. He lives with the Fairy Godmother. Sora, Donald and Goofy first meet Merlin when they are supposed to deliver an old book to him. Merlin appears in a puff of smoke to greet them. Merlin teaches Sora and his friends how to properly use magic. The upper level of his house is empty and can be used for magical training against enchanted furniture. Merlin also introduces Sora to the 100 Acre Wood (although Sora accidentally is pulled into the world through the book). If you complete certain tasks, Merlin will hand Sora and his friends magic themed weapons, such as the Spellbinder Keyblade, and the Dream Shield.

Kingdom Hearts: Chain Of Memories
Merlin is not mentioned and has not appeared in Chain Of Memories but it is assumed that he is still living in Traverse Town.

Kingdom Hearts II
Merlin now lives back in Hollow Bastion which is being rebuilt. He lives in a large cottage which seems to be the headquarters for the Hollow Bastion Restoration Committee. Merlin is part of the committee along with Leon, Yuffie, Aerith and Cid. Upon reuniting with Sora, he grants Sora and Donald the Blizzard element. Merlin gives Sora his first Summon charm which unlocks Chicken Little after he defeats the Hydra in Olympus Coliseum. Merlin also retrieves the 100 Acre Wood book from Traverse Town's Zero District and places it on a shelf in his house. Later, he travels to Disney Castle with Sora and co. to open up a magical door to the past. Merlin seems to have developed a rivalry with Cid, who prefers technology to magic, while Merlin prefers magic to technology. Their rivalry nearly gets out of hand when Cid calls Merlin an old man, and Merlin zaps Hollow Bastion's power computer, but thanks to Sora, Donald and Goofy, the town's systems are saved. Merlin and Cid later recall that Hollow Bastion was formerly called Radiant Garden and decide to rename it to its former name.

Origin
Merlin first and only appearance outside of Kingdom Hearts was in the 1963 film, The Sword In The Stone. In the film, Merlin teaches the young King Arthur some life lessons and prepares him for a life as the ruler of England. He also has a rivalry with Madam Mim, but this rivalry has yet to manifest in Kingdom Hearts. Merlin also has pet owl named Archimedes, who has not yet been seen in Kingdom Hearts, although his birdhouse is seen hanging in Merlins house in Kingdom Hearts II. Also, Archimedes can be heard calling outside of Merlins house in Kingdom Hearts.