Leader of men fools the people (6)
I believe the answer is:
masses
'the people' is the definition.
('masses' can be a synonym of 'people')
'leader of men fools' is the wordplay.
'leader of' suggests taking the first letters.
'fools' becomes 'asses' (ass is a kind of fool).
The first letter of 'men' is 'm'.
'm'+'asses'='MASSES'
(Other definitions for masses that I've seen before include "Christian church services for the many" , "Great numbers, at religious ceremonies?" , "The ordinary people" , "Services - large quantity (informal)" , "The common people generally" .)