First man to have a mad turn (4)
I believe the answer is:
adam
'first man' is the definition.
(first man in the Bible)
'a mad turn' is the wordplay.
'turn' shows that the letters should be reversed in order.
'mad' in reverse letter order is 'dam'.
'a'+'dam'='ADAM'
'to have' acts as a link.
(Other definitions for adam that I've seen before include "Male" , "father figure" , "Biblical progenitor of human race" , "expelled gardener" , "the first orphan?" .)