Father of Thor (4)
I believe the answer is:
odin
'father of thor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for odin that I've seen before include "Scandinavian war god" , "His son used bolts" , "Supreme Norse deity" , "Mythological Norse god of war" , "God - I nod (anag)" .)