Merlin: Ah, you know, lad, that love business is a powerful thing.
Arthur: Greater than gravity?
Merlin: Well, yes, boy. In its way... I'd say it's the greatest force on Earth.
~ Merlin to Arthur about love.
Merlin is an old wise magician and the deuteragonist of the 1963 Disney film, The Sword in the Stone. He helps a young Arthur become king but he also shows him the path of education and knowledge. He is tall, he wears all blue from head to foot and has a long white beard.
Merlin is living in a forest with his owl Archimedes. He adapts with his magic. He predicts a small boy will be arriving soon and joining him for tea. Wart is travelling through the dark woods trying to find an arrow and falls through the roof of Merlin's cottage. Merlin quickly befriends Wart and offers to tutor him all about education and learn all the courses of the world. Wart realizes he must return to his uncle's castle and Merlin decides to accompany him and pack up the cottage. With his magic, he stuffs everything in his suitcase and tallies off.
When they arrive at the castle, Merlin asks to be of service, but Wart's uncle refuses saying the boy has too many chores to have time to learn and asks Merlin to leave. Merlin disappears quickly which frightens Sir Ector and convinces Merlin to stay. As a recurring gag, Sir Ector keeps calling Merlin "Marvin" and gives the highest room in an old decaying tower. Sir Ector receives a visit from an old friend and Merlin sends Archimedes down to eavesdrop.
The owl disagrees and Merlin threatens to turn him into a human and he agrees. Archimedes learns that a jousting tournament will take place in London and the winner will be declared king. A few days go by and Merlin starts to see a bright future in Wart and tries to help him. He turns Wart into a fish and himself into a turtle and explores the wonders of the river in the castle moat. The two become attacked by a pike and Merlin becomes imprisoned in a knight's helmet, leaving Wart to deal with the fish himself. With unintentional help from Archimedes, Wart escapes and he and Merlin become human again.
When Wart returns to the castle, he is given double kitchen duty and forced to clean numerous pots and pans. Merlin appears and tells Wart that they should explore the wonders of being a squirrel. He then uses his magic to have the pots and pans clean themselves while they go off. Merlin turns him into a squirrel and turns himself into a rabbit and scurry around in the trees. A young female squirrel becomes infatuated with Wart and starts chasing him around the tree to get him to love her. Merlin joyfully sings a matchmaking song and a giant female squirrel comes up behind him and becomes infatuated with him. He tries to explain that he is human but she joyfully pushes him around.
To escape her, he falls down into a pile of leaves and emerges from him as a human to show he wasn't lying and the fat squirrel runs off scared. He then turns Wart back to normal which leaves the other squirrel heartbroken. Merlin then explain to Wart that love is a force more powerful than gravity.
When they return to the castle, Sir Ector and Kay are breaking the pots and pans in order to stop the magic but Merlin does so himself. Because of that, Ector throws him out and Merlin disappears. Wart is punished for defending Merlin and is no longer allowed to be Kay's squire for the jousting tournament. Merlin then appears before a distraught Wart and apologizes for what happened. He then told Wart that now he has a chance to be educated and Wart reluctantly agrees.
Archimedes volunteers to educate Wart while Merlin works on a mini-flying machine. The machine fails and Archimedes laughs about it. Wart tells how he fantasized flying and Merlin turns him into a little sparrow. Archimedes shows Wart how to fly and Wart ends up in Madame Mim's cottage. Mim prepares to kill Wart and Merlin abruptly storms in and accepts a duel with the witch.
Mim sets the rules saying that they can only turn into animals and cannot disappear. The duel begins with Mim turning into a crocodile and Merlin unintentionally turning into a turtle. To escape, Merlin quickly becomes a rabbit and Mim becomes a badger, chasing him again.
They run into a tree and Mim turns into a centipede and escapes through a little hole. Merlin runs out as a rooster and he bites her on the behind and hurls her in the air. To avoid being eaten, Mim then becomes a hippo and crushes him. She asks if he was okay and he becomes an elephant and tries to strangle her with his trunk. Mim then turns into a mouse and scares Merlin away but as she chases him he becomes a tiger and chases and captures her. Mim turns into a mongoose and Merlin tricks her into biting herself. She chases him down a large hole and out of the other but he blocks the whole with a rock and she bangs her head. Then Merlin turns into a crab and tries to grab Mim as she pops out but keeps missing.
After a few failed attempts, he grabs something which was a horn as Mim was now a rhino. With Merlin holding on, she charges towards a tree but he escapes in time and she becomes stuck in the tree. Merlin then becomes a goat, charges towards her and then rams her into the ravine below. Mim turns into a giant fire-breathing purple dragon and chases Merlin to which he turns into a rabbit again and she captures him, declaring herself the winner. Merlin disappears, but his voice could be heard saying that he has turned into a germ of a rare disease and infected Mim with it. He explains the symptoms, saying she has giant red spots, followed by hot and cold flashes and with violent sneezing. She throws a tantrum and becomes bedridden until further notice. Merlin suggests sunshine, opens up her roof and Mim yells saying she hates sunlight.
A few months later, Sir Ector changes his mind and makes Wart Kay's squire. Wart becomes enthusiastic and rushes to tell Merlin. Archimedes congratulates him but Merlin becomes furious saying all that learning will go down the drain and being a squire will not get him anywhere. He then loses control and literally shoots off and Archimdes explains he went on vacation to blow off steam. During his absence, Wart pulls the sword from the stone and is declared king. Afraid of the pressures of being a king, Wart yells out Merlin's name, begging for help and the wizard returns in tropical clothing. He becomes proud of Arthur and promises to help his monarchy.