I have been working with Merlin as one of my deities recently, so I have been doing some research on him. I found this article which is quite interesting:
The Legend of Merlin
During the Middle Ages the story of Merlin was popularized in the so-called Arthurian Romances, romantic tales first written in the twelfth and thirteenth centuries. These stories were set many years earlier, in the fifth century, when Britain was in turmoil after the end of Roman rule.
Historically, following the collapse of the Roman Empire Britain declined into anarchy; native warlords fought each other and, to make matters worse, the Anglo-Saxons from Denmark and Germany began to invade. According to the Arthurian Romances, it was Merlin who saved the Britons from this chaos.
In these tales the wise wizard cleverly contrives to make Arthur Britain's sole king, thus unifying the country against the invaders. Although there is peace for a while, the Britons are eventually drawn into civil war when Arthur falls sick and his knights argue amongst themselves. To reunite the country, Merlin devises a quest. He is guardian of the Holy Grail, a sacred cup that when drunk from can cure all ills. However, rather than simply let Arthur drink from the vessel, Merlin sends the knights in search of its secret hiding place, knowing that in their searching they will acquire the wisdom to again work as one. It is Sir Perceval who eventually finds the Grail; Arthur recovers, and the land is reunited. Merlin then retires to the mysterious Grail Castle where the relic is kept, appoints Perceval as the Grail's new guardian, and ultimately sails off to the secret isle of Avalon.
Although the Arthurian Romances were obviously embellished with fanciful detail, there is compelling evidence to show that, in essence, the story of Merlin was based on the life of an historical figure.
From the time the Roman Empire collapsed in the fifth century, until the Norman Conquest of 1066, civilization fell apart in Britain, and the country endured an era of chaos and warfare known as the Dark Ages. Few written records have survived from this time; consequently, the fifth century, when Arthur and Merlin are said to have lived, is an historical period steeped in mystery. The records that do survive only provide a rough outline of events, and most contemporary figures went completely unrecorded. Although, like Arthur, Merlin is mentioned in a few surviving Dark Age manuscripts, he is only referenced in passing. The first author to provide any actual detail concerning Merlin's life was the Welsh cleric Geoffrey of Monmouth who wrote in the 1130s. In his History of the British Kings Geoffrey introduces Merlin by saying that he first proved himself as a youth when a British king named Vortigern chose him as a sacrifice. According to Geoffrey, Vortigern was building a fort on a mountain in North Wales to protect his kingdom from the invading Anglo-Saxons, but each time the fort was close to completion the foundations mysteriously collapsed. Vortigern's advisors suggest that to put things right a boy must be sacrificed, and victim they pick is the young Merlin. However, just as Merlin is about to die, he tells the king that the problems are being caused by two dragons that dwell in a pool, in a cave below the fort's foundations. When the pool is discovered and the dragons released, Vortigern is so impressed by Merlin's mystic knowledge that he makes him his chief advisor and offers him the new fort as his own. Although this story is obviously an imaginative legend, a Dark Age manuscript records a similar story which reveals an historical figure behind the Merlin myth.
Vortigern was certainly an historical figure: he is recorded by Dark Age writers as the ruler of much of Britain in the mid-fifth century. Around the year 830 one Dark Age chronicler refers to King Vortigern when recounting a similar legend to Geoffrey's story of Merlin and the two dragons. In his History of the Britons the British monk Nennius wrote about a young man who saved himself being sacrificed by Vortigern by revealing that two dragons dwelt in a cave below the king's fort. The story is almost word-for-word that told by Geoffrey; the only difference is that the youth is not called Merlin, but Ambrosius. As both accounts are virtually identical, could this Ambrosius have been the man upon whom the stories of Merlin were based?
The dragon story was obviously an invention; Ambrosius, however, was not. Like Vortigern, he was an historical figure mentioned by other Dark Age writers. Although he is not record as a wizard, Ambrosius is recorded as uniting Britain in the post-Roman period. The work of a sixth-century monk named Gildas (The Ruin and Conquest of Britain, written around the year 545) refers to Ambrosius as a Roman aristocrat who led the British forces in their war against the invading Anglo-Saxons shortly after Vortigern's reign. Additionally, the English historian Bede (in his Ecclesiastical History of the English Nation, written in 731) says that Ambrosius' family name was Aurelius. The Aurelius family was a powerful Roman dynasty descended from the second-century Roman emperor Marcus Aurelius, and archaeology has shown that when the Roman legions departed members of this family remained in Britain. This Ambrosius Aurelius was therefore undoubtedly an historical figure, and the works of Geoffrey of Monmouth and Nennius taken together imply that Merlin was originally thought to be him.
Why, though, if Ambrosius was the historical figure behind the story of Arthur's wise advisor, has he gone down in legend under the name Merlin? The answer seems to be that the name Merlin was actually a title. Many British warriors of the time adopted the battle names of animals. The monk Gildas, for example, refers to a number of British kings of his time by such titles as the Lion, the Hound and the Leopard. Even the name Arthur seems to have been a title coming from the old British word Arth, meaning Bear. The name Merlin appears to derive from the old British meaning "the Eagle". (In fact, there is still a bird of prey called a merlin to this day.) A number of Dark Age poems are preserved as copies in a medieval manuscript known as The Red Book of Hergest, now in the Bodleian Library at Oxford University. One of these poems clearly demonstrates that Merlin was named after this bird: concerning a prediction Merlin is said to have made, it is entitled The Prophecy of the Eagle.
Ambrosius Aurelius does have many things in common with the Merlin of later romance. Like Merlin, he united Britain in the period after Vortigern's reign: both Gildas and Bede say that he successfully halted the invasion of Britain in the last few decades of the fifth century. There are no such records concerning what actually occurred in Britain immediately after Ambrosius' victories over the Anglo-Saxons, however; but as this is the time Arthur is said to have been king, it might well be that the aging Ambrosius relinquished power in favor of the younger Arthur and remained as his advisor. Also like Merlin, Ambrosius may have been regarded as a mystic.
Surviving writings concerning Britain in the Dark Ages are found mainly in Welsh manuscripts and in the Welsh language. The reason being that by the seventh century the Anglo-Saxons had resumed their offensive and successfully conquered what is now England. The native Britons were forced to retreat west, into what is now Wales. It was therefore here that most records concerning the earlier Dark Age period survived. The Welsh language developed directly from Brythonic, the language spoken throughout most of Britain in the immediate post-Roman period, while English developed from the language of the Anglo-Saxons. As the Welsh language had very different inflections to the English and Latin tongues, the Welsh had their own rendering of both Roman and English names, making them easier to pronounce. In Welsh writings the name Merlin appears as Myrddin, and Ambrosius is rendered as Emrys. (Ambrosius Aurelius is referred in Dark Age Welsh documents as Emrys Gwledig – "Prince Emrys".) One Dark Age Welsh reference actually links the names Myrddin and Emrys together. In a list of bards (Dark Age British poets) found in The Red Book of Hergest, one of the bards is called Myrddin Emrys – Merlin Ambrosius (see Triad 87). If this is the same person as Ambrosius Aurelius, then it means that the Britons at the time would almost certainly have regarded him as having mystical powers. Although today the word bard is associated simply with poets, during the Dark Ages bards were also accredited with the gift of prophecy, as was Merlin in the Arthurian Romances.
So where did this Merlin/Ambrosius live? According to Geoffrey of Monmouth, Vortigern gave Merlin his fort on a mountain in North Wales. Today, there is an identifiable location that might have been the mountain in question. A mountain in the North Wales Snowdonia range is still called Dinas Emrys – Fort Ambrosius. In the 1950s excavations near the summit uncovered the remains of a post-Roman fortification built sometime in the mid-to-late 400s, precisely the time Vortigern is known to have reigned and Merlin is said to have lived. There is, however, a more likely location.
The mountain of Dinas Bran (named after a pre-Christian Celtic god) stands close to the English Welsh border near the North Wales town of Llangollen. The ruins of the castle that still survive on the summit date from the thirteenth century, but archaeology has revealed that the hilltop had been fortified for many centuries before that. The earliest fort dates from around the mid fifth century so, like Dinas Emrys, it was probably built during Vortigern’s time. What makes this a more probable location for the fort in the story of Merlin and the two dragons is that it directly overlooks the heart of Vortigern’s kingdom in what is now Shropshire, just over five miles to the south-east. This is strategically a more feasible site: it stands on the edge of the Welsh Mountains, whereas Dinas Emrys, although possibly later used by Ambrosius to protect the Welsh coast from incursions by invaders from Ireland, is over fifty miles further west, on the other side of the Welsh mountains in an area the Anglo-Saxon’s never threatened.
So it seems that the story of Merlin was based on the life of Ambrosius Aurelius, an historical figure who united the Britons in the mid-to-late fifth century. He could well have been advisor to his successor King Arthur and, if he was a bard, he would have been accredited with the gift of prophecy.
Source - grahamphillips.net
The picture shown here is from www.legendarycreations.com I also have this image incorporated into a tattoo on my arm.