Sphere of the true leader of men (5)
I believe the answer is:
realm
'sphere' is the definition.
(I know that realm is a type of sphere)
'the true leader of men' is the wordplay.
'the true' becomes 'real' (I've seen this before).
'leader of' says to take the initial letters.
The initial letter of 'men' is 'm'.
'real'+'m'='REALM'
'of' acts as a link.
(Other definitions for realm that I've seen before include "Lamer (anag.)" , "Area of interest/activity" , "Empire - state" , "monarch's responsibility" , "the UK, perhaps" .)