battler vs gladiator

battler and gladiator both are nouns.

Word	Noun	Adjective	Verb	Adverb
battler	Yes	No	No	No
gladiator	Yes	No	No	No

As nouns, gladiator is a hyponym of battler; that is, gladiator is a word with a more specific, narrower meaning than battler:

battler: someone who fights (or is fighting)
gladiator: (ancient Rome) a professional combatant or a captive who entertained the public by engaging in mortal combat

battler (noun)	gladiator (noun)
someone who fights (or is fighting)	(ancient Rome) a professional combatant or a captive who entertained the public by engaging in mortal combat
	a professional boxer