King, say, eating good eggs up (6)
I believe the answer is:
george
'king' is the definition.
(eg King George VI)
'say eating good eggs up' is the wordplay.
'say' becomes 'eg' (both can mean 'for example').
'eating' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'eggs' becomes 'roe' (fish eggs).
'up' is a reversal indicator (in down clue: letters go upwards).
'g'+'roe'='groe'
'eg' enclosing 'groe' is 'egroeg'.
'egroeg' in reverse letter order is 'GEORGE'.
(Other definitions for george that I've seen before include "Ira's composer brother" , "Boy's name" , "Dragon-slaying saint" , "England's patron saint" , "Beatle" .)