Atop donkey is Greek millionaire (7)

I believe the answer is:

onassis

'greek millionaire' is the definition.

'atop donkey is' is the wordplay.
'atop' becomes 'on'.
'donkey' becomes 'ass' (ass is a term for a donkey).
'on'+'ass'+'is'='ONASSIS'

(Other definitions for onassis that I've seen before include "big name in shipping" , "Aristotle -, married Jackie Kennedy" , "First lady once" , "Greek businessman" , "Shipowner called Aristotle" .)

I've seen this clue in The Everyman puzzle in The Observer.

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