Theban who married his mother (7)
I believe the answer is:
oedipus
'theban who married his mother' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for oedipus that I've seen before include "King known for complex" , "Tragic king of Thebes (with a complex)" , "Legendary Greek king with mother complex" , "tragic hero" , "One who married his mother" .)