Don King's pursuing 50% of fortune (4)
I believe the answer is:
wear
'don' is the definition.
(I know that don can be written as wear)
'king's pursuing 50% of fortune' is the wordplay.
'king' becomes 'R' (abbreviation of Latin rex).
'pursuing' is a charade indicator (letters next to each other).
'50% of' means to take half the letters.
'fortune' becomes 'wealth' (both can mean riches or money).
'wealth' cut in half is 'wea'.
'r' put after 'wea' is 'WEAR'.
(Other definitions for wear that I've seen before include "Clothing; degrade" , "display" , "Tire; dress in" , "Durham river" , "Damage from use" .)