King Arthur was a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries AD. The details of Arthur's story are mainly composed of folklore and literary invention, and his historical existence is debated and disputed by modern historians.
That is a very controversial question. First of all, King Arthur was a king, not a knight. And if you mean who crowned King Arthur, then that would be his followers. And if you are referring to some point before his kingship, then it could be the Lady of the Lake, or Merlin. It all depends on which version of the story you mean, because there are hundreds.
