One beginning to make a mark as Muslim leader (4)
I believe the answer is:
imam
'muslim leader' is the definition.
(I've seen this in another clue)
'one beginning to make a mark' is the wordplay.
'one' becomes 'i' (Roman numeral).
'beginning to' says to take the initial letters.
'mark' becomes 'm'.
The first letter of 'make' is 'm'.
'i'+'m'+'a'+'m'='IMAM'
'as' is the link.
(Other definitions for imam that I've seen before include "Authority on Islamic doctrine and law" , "Muslim religious leader" , "Leader of prayers in mosque" , "Caliph" , "Muslim community leader" .)