Yami Sukehiro will not become the next Wizard King of the Clover Kingdom for various reasons. First, the current emperor, Julius Novachrono is still alive; and second, Fuegoleon will become the next Wizard King not Yami. Yami is a foreigner from Hino Country and the captain of the infamous Strongest Black Bull Members.

Is Captain Yami as strong as the Wizard King?

Exactly, and julios, the wizard king lost against litch \ Patry , and asta as well with Yuno defeated him, and also all of the captains cant compare to asta or Yuno exept Yami... ... The strongest amongst them holds the title of Wizard King.

Can Yami beat Julius?

I don't think Julius is stronger. But he's far faster, so he would definitely win against Yami. ... As the question of whether Yami is stronger he is very much the same amongst other captains the only thing that sets him apart is his ability to surpass his own limits and also the fact that he posses dark magic.