Russian kings (5)
I believe the answer is:
tsars
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">russian kings</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tsars that I've seen before include "Russian emperors" , "Old Russian rulers" , "Old Russia's rulers" , "Old monarchs" .)