Wielder of the hammer Mjölnir (4)
I believe the answer is:
thor
'wielder of the hammer mjolnir' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for thor that I've seen before include "can be classed as immortal" , "Imitative artistic work" , "Scandinavian god of thunder and the weather" , "Mythical figure" , "Germanic thunder god; early US IRBM" .)