Roman ruler put off by a scare (6)
I believe the answer is:
caesar
'roman ruler' is the definition.
(I've seen this before)
'off by a scare' is the wordplay.
'off' is an anagram indicator.
'by' means one lot of letters go next to another.
'a' after 'scare' is 'scarea'.
'scarea' with letters rearranged gives 'CAESAR'.
'put' acts as a link.
(Other definitions for caesar that I've seen before include "Top man" , "Old Roman emperor like Julius" , "A scare for Roman emperor" , "extraction operation" , "Augustus or Hadrian, say" .)