King Arthur probably lived, if he lived at all, in the century either side of the year 500. In popular legend he was a Romano-British military leader who fought against Anglo-Saxon invaders; met with his knights around a round table at a place called Camelot; proved his worth by pulling a sword from a stone; and invented chivalry. The wider picture in Scotland at the time is set out in our Historical Timeline.
Let's start with the obvious question: why does a web site about Scotland carry a biography of a possibly mythical person who everyone knows was based at Tintagel in Cornwall? The answer is that there are scholars who believe that the story of King Arthur, and just possibly the real man or men whose lives formed the basis of the story, originated in what is now Scotland. To be fair, many others believe that King Arthur was British, or Welsh, or Roman. Some even believe that he was Persian: that he was the leader of a Roman auxiliary cavalry unit raised in Samaria which went freelance and established a power base in northern Britain after the withdrawal of the Empire from these islands.
Historical evidence for the real Arthur is very slight. The Historia Brittonum, probably written by a Welsh cleric in the 800s, lists twelve battles it says were fought by Arthur, culminating in the Battle of Mons Badonicus or Mount Badon. The Annales Cambriae or "Welsh Annals", written in the 900s, also link Arthur with the Battle of Mount Badon which it dates to 516 or 518. For the year 537 it notes: The strife of Camlann, in which Arthur and Medraut fell. Medraut is more usually referred to as Mordred.
And that's it. Arthur received no mention from other early historians such as the British cleric Gildas, who in the late 500s wrote of the Battle of Mount Badon without mentioning Arthur. Nor does he appear in the Anglo-Saxon Chronicles produced from the 800s, or in Bede's history of England written in the early 700s, though Bede also mentions the Battle of Mount Badon.
The story of King Arthur only really begins with Geoffrey of Monmouth's Historia Regum Britanniae or "History of the Kings of Britain", completed in 1138. Monmouth was not a man to let the facts get in the way of a good story, and while he may have based some of his story of Arthur on traditional Welsh songs and poems, it seems likely he invented much of it.
Against this background, Arthur can be just about anyone you want, which is perhaps part of his appeal, and why his legend has taken such deep root in English, Welsh, Breton and even German mythology: and in Scotland.
Scotland offers a couple of candidates for identification as Arthur. One was Áedán mac Gabráin, King of Dalriada (roughly covering modern Argyll and possibly parts of northern Ireland) from 576 to 609. His burial on Iona is said to have given rise to the legend of Arthur's burial on Avalon. He lived a little too late if you take 516 and 537 as fixed dates, however, and is pretty unconvincing anyway.
Still later is Artuir mac Áedáin, eldest son of Áedán mac Gabráin. Artuir mac Áedáin does at least have a name that sounds right, and though never a king was a military leader in campaigns against the Anglo Saxon Northumbrians and against the Picts, who he was fighting when he died in 582. There are other parallels between Artuir and the legend of Arthur. He is said to have used as a base a Roman fort at Camelon near Falkirk, just conceivably Rough Castle on the line of the Antonine Wall. Camelon could have become distorted into "Camelot" over time, or into "Camlann", where Arthur and Mordred are recorded as being killed (though 45 years too early). An alternative theory would have Stirling Castle as Camelot.
Meanwhile, Artuir had a sister called Morgan (like Arthur), and was a contemporary of Myrddin Wyllt, one of two figures later combined to form the legend of Merlin. In the years from 573, Myrddin Wyllt was living as a mystic or madman, depending on your point of view, in Tweeddale in the Scottish Borders. To stretch the connection further, after his death in battle against the Picts, Artuir is said to have been buried at a place called Invalone (Avalon?), allegedly an island on the River Forth near Stirling.
At the time all this was happening, much of south west Scotland formed the Kingdom of Strathclyde, a British kingdom with very close cultural and linguistic links to Wales. Much of the theory of a Scottish Arthur depends on the retreat of British culture back to its Welsh heartland after Strathclyde was extinguished as an entity in the century either side of 1000: taking its legends with it, including the legend of Arthur.
If you subscribe to the idea of a Scottish Arthur, then it makes sense of a large number of Scottish place names involving "Arthur", most notably Arthur's Seat in Edinburgh, as well as Ben Arthur and Loch Arthur. It also makes slightly more sense of a traditional story surrounding a carving on a Pictish stone found at Meigle in Angus and still on view in the museum there. This shows a person surrounded by four animals. It is said to show King Arthur having Queen Guinevere killed by wild animals because he believed she had been unfaithful to him while being held captive by Mordred, who in this version of the story is a Pictish King: albeit one who avoided being mentioned on any of the Pictish king lists produced by early chroniclers. This carving is actually more likely to depict the biblical story of Daniel and the lions, but the link with Arthurian legend is interesting.
Guinevere herself is said to have come from Perth. Meanwhile Sir Lancelot is said to have come from the Lothians, possibly associated with Traprain Law or with another candidate for Camelot, Tantallon Castle: while Sir Gawain is said to have been the son of Artuir/Arthur's sister Morgan and King Lot of Orkney. There is also a traditional site for King Arthur's grave in the Eildon Hills south of Melrose, where he is said to sleep with an army of warriors ready to rise again when called: and Merlin is said to be buried at Drumelzier, close to the River Tweed and close to a tiny settlement called Merlindale.