-ator +

(Latin: a suffix that forms masculine nouns from verbs)

arbitrator (s) (noun), arbitrators (pl)
Someone who hears both sides of a dispute and then makes a decision: An arbitrator acts like a judge and determines which side is right.

Both of the authors agreed to accept a decision by an impartial arbitrator as to which book would be published first.

Last year in the case of the divorce, the judge acted as the arbitrator by deciding which parent the children would live with.

astrogator
Someone; usually a man, who navigates in outer space either in interplanetary travel or in interstellar travel.
auscultator
A person who performs auscultation; that is, someone who uses a procedure for detecting certain defects or conditions by listening for normal and abnormal heart, breath, bowel, fetal, and other sounds in the body.
aviator (s) (noun), aviators (pl)
Someone or those who operate an aircraft.

Refashioned after French aviateur. See aviation for origin of this word.

dictator (s) (noun), dictators (pl)
1. A person exercising absolute authority of any kind or in any sphere; one who authoritatively prescribes a course of action or says what is to be done: When a country is run by a dictator, he or she has total and complete command over the people and can often be very cruel.
2. A person who tells a writer what to put into print: When Johann Sebastian Bach was very old and became blind, he acted as a dictator when he told his son-in-law to write down the notes for his music.
emancipator (s) (noun), emancipators (pl)
Someone who frees others from bondage or slavery: Abraham Lincoln is known to have been the Great Emancipator.
gladiator
1. A person, usually a professional combatant, a captive, or a slave, trained to entertain the public by engaging in mortal combat with another person, or a wild animal, in the ancient Roman arena; now more like a person engaged in a controversy or debate, especially in public; a disputant.
2. In ancient Rome, a professional fighter who fought another combatant, or a wild animal, in public entertainments which took place in an arena.

Often gladiators were criminals, or slaves, who were equipped with nets, nooses, swords, or other weapons for battle to entertain Romans in the circuses.