Geoffrey's rendering of the character was immediately popular, especially in Wales. Later writers expanded the account to produce a fuller image of the wizard. Merlin's traditional biography casts him as a cambion: born of a mortal woman, sired by an incubus, the non-human from whom he inherits his supernatural powers and abilities. The name of Merlin's mother is not usually stated but is given as Adhan in the oldest version of the Prose Brut. Merlin matures to an ascendant sagehood and engineers the birth of Arthur through magic and intrigue. Later authors have Merlin serve as the king's advisor until he is bewitched and imprisoned by the Lady of the Lake.
Human merlin is coded by the gene NF2 in Chromosome 22. Mouse merlin gene is located on chromosome 11 and rat merlin gene on chromosome 17. Fruit fly merlin gene (symbol Mer) is located on chromosome 1 and shares 58% similarity to its human homologue.
Other merlin-like genes are known from a wide range of animals, and the derivation of merlin is thought to be in early metazoa. Merlin is a member of the ERM family of proteins including ezrin, moesin, and radixin, which are in the protein 4.1 superfamily of proteins. Merlin is also known as schwannomin, a name derived from the most common type of tumor in the NF2 patient phenotype, the schwannoma.
Vertebrate merlin is a 70-kDa protein. There are 10 known isoforms of human merlin molecule (the full molecule being 595 amino acids in length). The two most common these are also found in the mouse and are called type 1 and type 2, differing by the absence or presence of exon 16 or 17, respectively). All the known varieties have a conserved N-terminal part, which contains a FERM domain (a domain found in most cytoskeletal-membrane organizing proteins). The FERM domain is followed by an alpha-helical domain and a hydrophilic tail. Merlin can dimerize with itself and heterodimerize with other ERM family proteins.
After the King of England, Uther Pendragon, dies, leaving no heir to the throne, a sword appears inside an anvil in London. The sword bears an inscription proclaiming that whoever removes it will be the new king. No one can remove the sword, which is eventually forgotten, leaving England in the Dark Ages.
Years later, a 12-year-old orphan named Arthur, commonly called Wart, accidentally scares off a deer his foster brother Kay was hunting, causing Kay to launch his arrow into the forest. In retrieving the arrow, Arthur lands in the cottage of Merlin the wizard, who declares himself Arthur's tutor and returns with the boy to his home, a castle run by Sir Ector, Arthur's foster father. Ector's friend, Sir Pellinore, arrives with news that the annual jousting tournament will be held on New Year's Day in London, and the winner will be crowned king. Ector decides to put Kay through serious training for the tournament and appoints Arthur as Kay's squire.