Playwright's retrospective to depict old, cold Spanish kingdom (4,6)
I believe the answer is:
noel coward
'playwright's' is the definition.
(I've seen this before)
'retrospective to depict old cold spanish kingdom' is the wordplay.
'retrospective' says the letters should be written backwards.
'to depict' becomes 'draw' (synonyms).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'cold' becomes 'C' (eg on taps).
'spanish kingdom' becomes 'leon' (Kingdom of Len).
'draw'+'o'+'c'+'leon'='drawocleon'
'drawocleon' back-to-front is 'NOEL COWARD'.
(Other definitions for noel coward that I've seen before include "Old playwright" , "He wrote" , "dramatist" .)