Complex fellow takes fish back into work (7)
I believe the answer is:
oedipus
'complex fellow' is the definition.
(namesake of the Oedipus complex)
'fish back into work' is the wordplay.
'fish back' becomes 'edi' (I can't justify this - if you can you should believe this answer much more).
'into' means one lot of letters goes inside another.
'work' becomes 'opus' (an opus is an artistic work).
'edi' inserted within 'opus' is 'OEDIPUS'.
'takes' acts as a link.
Can you help me to learn more?
(Other definitions for oedipus that I've seen before include "Mythical Greek king of Thebes" , "One who married his mother" , "He solved Sphinx's riddle" , "Mythic king who killed his father and married his mother" , "person who married his mother" .)