Ruler using old rover moving around (8)
I believe the answer is:
overlord
'ruler' is the definition.
(I know that overlord is a type of ruler)
'old rover moving around' is the wordplay.
'moving around' indicates an anagram.
'old'+'rover'='oldrover'
'oldrover' with letters rearranged gives 'OVERLORD'.
'using' acts as a link.
(Other definitions for overlord that I've seen before include "Old rover (anag.)" , "Feudal superior" , "Feudal ruler" , "Wartime operation" , "Supreme ruler" .)