Norwegian king (4)
I believe the answer is:
olaf
'norwegian king' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for olaf that I've seen before include "Name of five kings of Norway" , "Scandinavian monarch" , "Man's name; foal (anag.)" , "King and patron saint of Norway" , "St ---, Norwegian king" .)