King Arthur is based on a historical Romanized Celtic general (Named Arturus) fighting to protect his homeland from the invading Angles and Saxons. Merlin is not a historical figure but a fictional character based on both another Romanized Celtic warrior and a medieval madman.
its a myth like robin hood they reckon in 200 yrs time ppl will think harry potter was real to
They are fiction. Neither King Arthur nor Merlin ever existed.
It's mostly legend & myth. It's speculated that King Arthur may have been a "Romanized" celt who took over the leadership of Britain after the Romans left in 410 CE & died while defending against Saxon invaders. They also speculate that maybe Merlin was a celtic druid from beyond the old Roman borders who allied his people with Arthur against the Saxons. But this is all speculation; there is no historical evidence for this story whatsoever.