The most common and most likely answer to this crossword clue is the 7 letter word EMPEROR
I've seen this crossword clue in The Times
E
M
P
E
R
O
R
More clues leading to the result EMPEROR
- Augustus was one heading off moderate men
- English Queen entertaining politician, or another monarch
- Ruler pre-Rome? That must be wrong
- Caesar’s backing representative in his city
- Ruler in mood beheaded soldiers
- Salesman in European capital recalled title
- Ruler in mood executed soldiers
- Ruler exercises right during more rioting
- Representative in European city upset ruler
- Traveller in capital backing sovereign
Buddy explains!

The straight part
We know that "Ruler" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ruler = emperor.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EMPEROR mean?
EMPEROR noun- The male monarch or ruler of an empire.
- Any monarch ruling an empire, irrespective of gender, with "empress" contrasting to mean when consort to emperor
- (political theory) Specifically, the ruler of the Holy Roman Empire; the world-monarch.
- The fourth trump or major arcana card of the tarot deck.
- A large, relatively valuable marble in children's games.
- Any fish of the family Lethrinidae.
- Any various butterflies of the subfamily Charaxinae.