"Yeah there is a king of magick, he is 10 ft 2 with a long beard that is 5ft 8, and he wears a crown upon his worn out pointy hat, oh yeah and he wears blue robes and has wings."
Sorry, there is no king of magick. If so there would be constant bickering about what he thinks is good, and what's not.
Also Magi aren't unified. Considering the Magi alone a civilzation we are more tribal than imperial.
I would say it depends what community you are in. Wicca for example uses the term in a very limited way.
Alex Sanders, for instance, referred to himself as a King because he founded the Alexandrian Tradition of Wicca. Gardner, however, hated that idea and refused to use it. Hence use of the fond nickname Uncle Gerald, instead.
In any of the British Wiccan Traditions, there are senior Elders who may fall under the title of Witch Queen. Different Traditions hold differing requirements for this. In some cases, a High Priestess with three daughter covens qualifies as a Queen. In other Traditions, a Queen is the head of particular lineages or geographic area.
That said, the title of King is never used because the term King refers to the Holly and Oak Kings of the Wheel of the Year.
King Kevin of the UK is none of these - he's just another man with a big ego and a bathrobe.