Like ruler to be demanding (6)
I believe the answer is:
asking
'be demanding' is the definition.
(I've seen this before)
'like ruler' is the wordplay.
'like' becomes 'as'.
'ruler' becomes 'king' (king is a kind of ruler).
'as'+'king'='ASKING'
'to' acts as a link.
(Other definitions for asking that I've seen before include "For the ___; freely available" , "Questioning" , "Presenting petition" , "Appealing" , "Inquiring" .)