Lower classes see one ruling cruelly (6)
I believe the answer is:
despot
'one ruling cruelly' is the definition.
(a despot is a cruel ruler)
'lower classes see' is the wordplay.
'lower classes' becomes 'de' (I've seen this in other clues).
'see' becomes 'spot' (to spot is to notice or catch sight of).
'de'+'spot'='DESPOT'
(Other definitions for despot that I've seen before include "Gaddafi, say" , "Posted (anag)" , "Tyrannical dictator" , "who treats others badly?" , "Possibly 4 [CZAR]" .)