Traveller in capital upset ruler (7)
I believe the answer is:
emperor
'ruler' is the definition.
(I know that emperor is a type of emperor)
'traveller in capital upset' is the wordplay.
'traveller' becomes 'rep' (travel company worker).
'in' is an insertion indicator.
'capital' becomes 'rome' (capital of Italy).
'upset' shows that the letters should be reversed in order.
'rep' going inside 'rome' is 'rorepme'.
'rorepme' back-to-front is 'EMPEROR'.
(Other definitions for emperor that I've seen before include "Ancient Roman ruler" , "Large richly coloured butterfly" , "Pre-Rome (anag.)" , "Monarch" , "Large richly-coloured butterfly" .)