Porter maybe for an old king (4)
I believe the answer is:
cole
I believe this clue is a double definition.
'porter maybe' is the first definition.
(musician Cole Porter)
'an old king' is the second definition.
(nursery rhyme character Old King Cole)
'for' acts as a link.
(Other definitions for cole that I've seen before include "Old English king!" , "Old nursery rhyme king" , "Cabbage" , "Elderly monarch" , "died in 2015" .)