Magic King

A "Magic King" is an abstract concept that circles the magical community. Though very few wizards can agree as to what a Magic King is in practice, all can agree that they are a "Supremely Powerful Wizard". Becoming a/the Magic King is the ultimate goal of a number of wizards, notably Connor Regulas of the Gryphon Wing Guild.

Overview
The term "Magic King" has existed for almost as long as knowledge of Magic itself. Though the actual meaning of the term, the significance of the "Magic King" to the world and whether or not the Magic King a title unique to a single individual or was passed down to a number of wizards.

Gonzen's Theory
Gonzen, the magical instructor of Connor Regulas, his brother as well as the wizard Rikon Alo, theorized that the term "Magic King" was once bestowed upon the most powerful wizard in the world, and they were referred as the "King" because they possessed power enough that all wizards bowed before them...willingly, begrudgingly and through extreme force. Gonzen does note, however, that the title hasn't been used since a time before the rise of various Magic Councils, or even the time of Zeref.

Sephirus's Theory
Sephirus Alpha, or at least her lingering spirit, offered an alternate theory as to the true nature of the Magic King; that they were a literal Monarch reigning over all Wizards. She claimed that her theory was substantiated, and that her claim to the title itself proven, through the existence of the Royal Element Magic, a potent form of Anti-Magic that had been passed down through her family for centuries.