King Arthur's magician (6)
I believe the answer is:
merlin
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">king arthur's magician</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for merlin that I've seen before include "Arthur's sorcerer" , "Arthur's adviser" , "small aggressive bird of prey" , "Hawk-like magician of Camelot" , "Arthurian wizard" .)