Painter of a human extra-terrestrial! (5)
I believe the answer is:
manet
'painter' is the definition.
(I've seen this before)
'a human extra-terrestrial' is the wordplay.
'a human' becomes 'man' ('man' can be a synonym of 'human').
'extra terrestrial' becomes 'et' (abbreviation - like in the famous m98a movie).
'man'+'et'='MANET'
'of' acts as a link.
(Other definitions for manet that I've seen before include "artistic individual" , "French painter" , "Edouard -- (artist)" , "Painter of Le Dejeuner sur l'herbe, d. 1883" , "Edouard - - (painter)" .)