IPA: /ɪmˈpɛrətər/
KK: /ɪmˈpɛrətər/
A title used in ancient Rome for a commander of an army or the supreme leader of the state, especially during the Roman Empire.
Julius Caesar was declared imperator after his military victories.
Imperator is derived from "imperare" (meaning to command) and the suffix "-tor" (indicating an agent or doer). The term originally referred to a commander or one who has the authority to command, particularly in a military context.
Think of someone who 'commands' ('imperare') — that's why an 'imperator' is a commander or leader.