Demanding, like ruler (6)
I believe the answer is:
asking
'demanding' is the definition.
('ask' can be a synonym of 'demand')
'like ruler' is the wordplay.
'like' becomes 'as'.
'ruler' becomes 'king' (king is a kind of ruler).
'as'+'king'='ASKING'
(Other definitions for asking that I've seen before include "Questioning" , "Appealing" , "Inviting (to an event)" , "Demanding" , "Inquiry" .)