Ok, here's what I got. Do note first of all, that it's all a bit confused. There's some agreement on the literature (often, but not always!) - and that's the only feature we can immediately hope to get any
definite information from! Which hardly bodes well for the rest...
But here's what I've collected:
The first real source Arthurian Literature (as we know it) seems to be Geoffrey of Monmouth's
Historia Regnum Brittaniae, which most likely appeared during the first half of the 12th century AD (Geoffrey died in 1155).
However, Lancelot didn't actually appear until a few years later. It was Chretien de Troyes, who wrote in the second half of the 12th century, who actually introduced a lot of the familiar names - Camelot, Lancelot, and Percival.
Lancelot was apparently first popularised in the Chretien story "The Knight and the Cart". Chretien also popularised the entire "Grail Quest" in "Cont du Graal", and it's interesting to note that Lancelot's adultery was originally with Mordred.
Galahad actually appears to be a slightly later addition than most knights (Gawain had his origins at least in Geofrey's, but possibly before) and Galahad was seemingly constructed simply to make a point that the other knights couldn't serve.
Note also that knights who achieved the Grail in other stories all failed in the "Lancelot Grail". It's the Lancelot Grail cycle that Mallory was using as a basis for much of his Morte D'Arthur, which is of course the most famous version of the story.
There's a lot of debate as to Lancelot's own origins - the whole issue seems very confused. On the one hand, some say that he's a purely Norman invention - but others insist on an Anglo-Saxon origin.
Add to that there are some other interesting theories around - there's especially a good one that the basis for the whole Arthurian legend is actually Sarmatian.
On this latter vein it is claimed that chivalry first appeared in the Caucasus Mountain region among the Alans, who are probably descended from the ancient Sarmatians, a people of the North Caucasus area who speak a language belonging to the Iranian language family.
Still with this theory, it is claimed that the essential outlines of the Arthurian story were known in Alan legend back in Roman times. There was a legion of Sarmatian soldiers, a tribe called Iazyges, from the steppes just north of the Caucasus who served in the Roman army and were transferred to Britain. The modern-day descendants of the Alans are thought to be the Ossetes.
It's also interesting to note that Plutarch apparently refers to a legend among the Britons "that the god Kronos slumbered on an island, guarded by Briareus" and that this has some bearing on the origin and development whole Arthurian legend.
While such ideas as the Sarmatian source are interesting as conjecture, it must be noted that there is no single overall convincing theory. Quite possibly, the early Arthurian writers such as Georfrrey and Chretien, were drawing not on any single legend, but instead wrote a fictional framework filled with details whimsically drawn from a range of
different traditions - from local Britain and homeland France (not to mention any other external lores the Norman's picked up elsewhere) - and peppered it all together with a good liberal sprinkling of self-fulfilling propaganda.
So essentially there never has been any single individual who could fulfill the critieria of being a Lancelot or Galahad - or even an Arthur. But there are always figures from history who will fill some archetypical requirements, but never wholly.
Some links (please note that they don't always agree with one another!):
Chretien de Troyes "Knight of the Cart" :
http://camelot.celtic-twilight.com/...en/lancelot.htm
Some history:
http://www.britannia.com/history/timeart2.html
Info about Galahad:
http://www.lib.rochester.edu/camelot/galmenu.htm
A good chronology for "what was published when?" :
http://phoenix.marymount.edu/~csnyder/Chronology.htm
And a generally helpful list of links:
http://www.arthuriana.co.uk/links/arthlink.htm
From Scythia to Camelot - Amazon
http://www.amazon.com/exec/obidos/ASIN/0815335660/ref=ase_dragonlordsofdumA/103-4884519-7652609
Essay on the above:
http://www.mun.ca/mst/heroicage/issues/2/ha2tf.htm
ALSO!
Note the following:
General Arthurian links and ersources:
http://people.bu.edu/agrhill/arthur.htm
The Modena Archivolt - an early 12th century engraving, which refers to "Artus de Bretania" (Arthur of Britannia).
http://camelot.celtic-twilight.com/sgmaoa/sculpture1.htm
Hope that helps.
