Source of genius found in poor Creole painter (2,5)
I believe the answer is:
el greco
'painter' is the definition.
(thesaurus)
'source of genius found in poor creole' is the wordplay.
'source of' indicates taking the first letters.
'found in' means one lot of letters goes inside another.
'poor' is an anagram indicator.
The first letter of 'genius' is 'g'.
'creole' is an anagram of 'elreco'.
'g' placed inside 'elreco' is 'EL GRECO'.
(Other definitions for el greco that I've seen before include "Spanish painter born 1541 in Crete" , "Cretan-born Spanish painter, d. 1614" , "Spanish Renaissance painter" , "Famous painter's nickname" , "Spanish painter born in Greece" .)