Merlin is a wizard, and is widely considered to be the most powerful in the world. He is a very wise character who believes in the philosophy of "Brain over Brawn". Merlin is shown to have a wide variety of abilities including the ability to see into the future, the ability to enchant various objects and people, and the ability to travel through time, among other powers. Despite his power, he can be absentminded and forgetful.
Merlin is first seen in his forest cottage, preparing afternoon tea. He predicts that a young boy will soon join him, but he doesn't quite know who. He later meets a pre-teenagaed orphan called Arthur, who is commonly known as the Wart. Merlin speaks to the Wart about the value of an education. Merlin decides to appoint himself as the Wart's tutor, and displays his magical abilities by shrinking all his possessions so that they fit into a small carpet bag.
Merlin accompanies the Wart to the castle of the Wart's foster father Sir Ector. Though Sir Ector initally disapproves, Merlin is able to persuade him though a display of magic. Merlin, who is confusedly called "Marvin" by Ector, is provided the "guest room", which is apparently a crumbling, teetering tower.
The next day, Merlin begins the Wart's education, teaching him the principle of brain over brawn by transforming the Wart into a fish. During the adventure Merlin, also in fish form, is trapped in an old helmet, while the Wart is chased by a giant pike. Merlin forgets the magic words to change them both back, but remembers just in time.
Later, Merlin goes to retrieve the Wart for another lesson, but the Wart is being forced to clean as punishment for being late as a result of the previous lesson. Merlin uses his magic to enchant the various kitchen objects into cleaning themselves, and sneaks the Wart out. Merlin transforms himself and the Wart into squirrels, where they live the dangerous life of the creatures. Merlin and the Wart are both pursued as mates by 2 female squirrels. Merlin grows increasingly annoyed and finally transforms into a human out of anger. He then transforms the Wart, much to the sorrow of the young female squirrel who had been chasing the boy.
Back at the castle, Merlin is insulted by Sir Ector, who believes that Merlin's magical enchantment of the kitchen objects is black magic. When the Wart protests, Sir Ector angrily forbids the Wart from making a future trip to a London tournament as Kay's squire. After seeing the Wart's sadness, Merlin apogizes, but suggests that the Wart use the opportunity to further his studies.
Merlin begins by talking of various happenings of the future, but the poor boy is so confused that Archimedes decides to take over the Wart's education. Despite Merlin's annoyance, he is later pleased to see the boy learning to write with Archimedes's help. Merlin takes the opportunity to show the Wart a model airplane. The plane fails to fly though, because the properller becomes caught in Merlin's long beard. The Wart appreciates the demonstration anyway, and confides that he dreams of flying. Merlin decides to turn the Wart into a small bird. The Wart then goes flying with Archimedes.
After being told of the Wart's capture by Madam Mim, Merlin appears. Mim angrily challenges Merlin to a Wizard's Duel, where he turns into a turtle, a rabbit, a walrus, a caterpillar, a goat, a crab and a mouse. Though initially at a disadvantage, Merlin wins by cleverly transforming into a germ.
Later, the Wart happily informs Merlin that he has been reinstated as the squire to Kay. Merlin is angry, as he thought the Wart had put aside war games in favor of learning. When the Wart explains that a postion as a squire is best hope, Merlin angrily turns into a rocket and travels to Bermuda. Later, he returns to where he is pleased to find that the Wart is now King Arthur.
Merlin will soon join the Shell Louge Squad in Spongebob and Friends and the Sword in the Stone, as he is reveled that he and several other wizards took part as the great heroes of the first cartoonian war, and may become the most impourent and powerful member of the shell louge squad, and the villain leage's greatest enemy.