Salesman in Rome, returning as leader (7)
I believe the answer is:
emperor
'leader' is the definition.
(I know that leader can be written as emperor)
'salesman in rome returning' is the wordplay.
'salesman' becomes 'rep' (sales representative).
'in' means one lot of letters goes inside another.
'returning' says the letters should be written in reverse.
'rep' inserted inside 'rome' is 'rorepme'.
'rorepme' backwards is 'EMPEROR'.
'as' acts as a link.
(Other definitions for emperor that I've seen before include "Male ruler of a group of countries" , "Roman leader" , "Ruler; butterfly" , "Largest type of penguin" , "Ruler of large territory" .)