Merlin enchants Uther to look like Gorlois and helps him to sleep with Igrayne, conceiving Arthur in the process. He then arranges for Arthur to be fostered by Sir Ector.
When Merlin places the sword in the stone in a churchyard in London, he writes an inscription saying that the person who can pull it out is King of England.
In the guise of an old man, Merlin informs Arthur of his parentage. Then, disguised as a young boy, he tells Arthur about Mordred, who will one day be the downfall of Arthur's kingdom.
Merlin helps Arthur to find Excalibur, the sword that enables him to defeat whomever he wields it against.
In the "Tale of Balyn and Balan," Merlin warns Balyn that he will strike a dolorous stroke that will destroy a kingdom, and then rescues him from a castle when that very same dolorous stroke causes it to fall.
Despite his many misgivings, Merlin arranges for Arthur to marry Gwenyvere.
Finally, Merlin falls in love with Nenyve, who imprisons him in a rock when she tires of his attentions. And so goes Merlin.