Crossword Genius

Grim villain, therefore overturned (4)

Ross

I believe the answer is:

ogre

I'm a little stuck... Click here to teach me more about this clue!

'grim villain' is the definition.
'ogre' can be an answer for 'villain' (I've seen this in another clue). I am not certain of the 'grim' bit.

'therefore overturned' is the wordplay.
'therefore' becomes 'ergo' (I've seen this in another clue).
'overturned' is a reversal indicator.
'ergo' in reverse letter order is 'OGRE'.

Can you help me to learn more?

(Other definitions for ogre that I've seen before include "Monstrous creature" , "Cruel, fearsome person" , "Cruel giant of folklore" , "The giant is some goer" , "terrible person" .)

I've seen this clue in The Telegraph.
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