Merlin, as he is usually known in English, or Myrddin in Welsh, was the chief magician, father-figure, and architect of King Arthur's life and reign.

Merlin Ambrosius, to give him his full name, was probably born in Carmarthen, south-west Wales.

In Y Gododdin, a work from the early 10th Century by Nennius, he is described as being a prophet. Merlin was the illegitimate son of a princess of Dyfed. His mother was a pious Christian, but his father was an incubus or devil that seeks to impregnate sleeping women.

In Merlin, written by Robert De Boron in the 13th Century, Merlin figures as an anti-Christ figure, born of an incubus to undo the holy life and good work introduced into the world by Jesus. This explain Merlin's magical or miraculous powers. But, despite the devil's best laid plan to have an evil child born on earth, Merlin is saved from being what the devil wanted him to be, through being baptised. Britain has its own miraculous-prophet.

Merlin came to prominence as a youth, when Vortigern, king of Britain, was in Snowdonia fighting the insurrections of local princes and fleeing from Saxon invaders.

The high-king of the Britons wanted to build a tower for protection at Dinas Emrys in Wales, but it kept falling down every time he tried. The king asked his wise men what to do, and their advice was for the king to sacrifice a fatherless boy. The young Merlin was chosen.

But before he was sacrificed, Merlin told the king that his tower was falling own because there was a deep underground pool of water beneath its foundations, which housed two dragons. One dragon was red (signifying the British) and the other white (the Saxons). The king ordered digging to commence beneath his building. Soon the spring was found. Merlin was vindicated.

But when many dragons, white and red, sprang out, it was Merlin who uttered prophesies. The dragons fought, with the white dragon having the best of it, at first, but then the red dragon drove the white one back. The meaning was explained. Merlin prophesied that Vortigern would be slain and followed on to the throne by Ambrosius Aurelianus, then Uther, then a leader greater than them all would appear to rescue the British. This mantle would fall upon this future king to drive the Saxons. Now, that Merlin knew the future, he had real power. He had come of age. His mission was about to begin.

Later, in accordance with Merlin's prophecy, Vortigern was defeated in battle by the Saxons, and Ambrosius became king. After many British nobles were tricked and slain by Saxons, the new vowed to erect a fitting monument. Merlin told the king to send his men to fetch stones from Ireland. The men came back with the giant stones that were erected on Salisbury Plain at Stonehenge.

After Ambrosius's death, the new king was Uther. Merlin realised that the land was threatened, and that it would one day need a king to unite all and to save the land from its enemies. So Merlin began to conceive of a secret plan.

After Ambrosius's death, the new king was Uther Pendragon. Merlin realised that the land was threatened by the instability of the new ruler, and that it would one day need a king to unite all and to save the land from its enemies. So Merlin began to plan.

King Uther Pendragon became obsessed with Igraine, wife of Gorlois, Duke of Cornwall. Uther lusted wildly after her, and when Gorlois locked her up for security in Tintagel Castle in Cornwall, Uther invaded his lands.

Gorlois defended this impregnable castle from his fortress at Dimilioc But Merlin made Uther to resemble Gorlois. So when Gorlois returned, as Igraine believed the man in her bower to be, she took him to her bed, and King Arthur was conceived.

Merlin took the newborn baby away to be looked after and brought up by Sir Ector, who groomed him to be a young squire. But Merlin was always close by.

As the years passed, the kingdom was indeed becoming fractious and the land was dying. The king was failing to unite and lead his people.  Merlin's vision was becoming true. When Uther Pendragon died, there was no one to inherit the kingdom, the land would go to waste, and the future looked bleak. It was time for a new king.

Kay, the son of Sir Ector, was competing at a tournament. Arthur was his squire.

Just before Kay was to fight, Arthur discovered that he had failed to bring Kay's sword. So when he came upon a sword in a stone, he drew it out to give it to Kay. Sir Hector saw this. He was amazed; he knew what it meant. Arthur drew the sword from the stone once more for all to see. Arthur was proclaimed king of all England. Merlin had secured the land and its people through his choice of king.

After his work was done securing the throne for the new king, Merlin became infatuated by Nimue (elsewhere called Viviane), according to Thomas Malory. He recklessly taught her magical secrets, which she used to imprison him. Geoffrey of Monmouth, in Vita Merlini or The Life of Merlin, says that Merlin stayed with King Arthur throughout his reign; directing the work of the king; strengthening him amidst his men; guiding him defend his country. And, finally, he was with King Arthur after the king's last battle, the Battle of Camlann. As King Arthur lay mortally wounded, surrounded by black robbed maidens. Merlin watched as the king was placed on a barge, and finally floated across the lake to the Isle of Avalon.

Stories of Merlin's madness occurs mainly in the Welsh Arthurian legends. Giraldus Cambrensis or Gerald of Wales says Merlin was at the battle of Arturet, but because he saw such terrible things in the sky, he left to live in the woods, as a wildman.

Many places claim to house Merlin's tomb. One such claim is for Merlin's Mound at Marlborough College, Wiltshire. On the dramatic, windswept coast of north Cornwall, Merlin's ghost is said to reside in Merlin's Cave, at the foot of Tintagel Castle.

Merlin has remained a source of fascination and inspiration to many people.