Ancient ruler's stable and popular heading for election (11)
I believe the answer is:
constantine
'ancient ruler's' is the definition.
(Roman emperor)
'stable and popular heading for election' is the wordplay.
'stable' becomes 'constant' (associated in meaning).
'and' is a charade indicator (letters next to each other).
'popular' becomes 'in' ('in' can mean trendy).
'heading for' indicates taking the first letters.
The first letter of 'election' is 'e'.
'constant'+'in'+'e'='CONSTANTINE'
(Other definitions for constantine that I've seen before include "First Christian emperor" , "Great man" .)