Mad character's mad threat (6)
I believe the answer is:
hatter
'mad character's' is the definition.
(Alice In Wonderland)
'mad threat' is the wordplay.
'mad' is an anagram indicator.
'threat' with letters rearranged gives 'HATTER'.
(Other definitions for hatter that I've seen before include "Tea Party member" , "Tea-party holder" , "Maker of headwear" , "Threat (anag)" , "supplying pork pies?" .)