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Native American and Asian warriors from minor tribes have their attack and hitpoints greatly increased.
—In-game description

Legendary Native Warriors (Exalted Natives for Asian civilizations) is a technology in Age of Empires III that can be researched in the Capitol by European civilizations or the Town Center by Native American and Asian civilizations once the Imperial Age is reached. Once researched, it upgrades native warriors to the Legendary/Exalted level, increasing their hit points and attack by 50%. Unlike native units' Elite/Disciplined and Champion/Honored upgrades, this technology costs food and wood.

Note that if Legendary Native Warriors/Exalted Natives is researched without researching the native warriors' Elite/Disciplined and/or Champion/Honored upgrades at the Trading Post first, they will have less hit points and attack. Researching the upgrades will improve them, but they'll be considered to be upgraded to the corresponding level(s), although this does not affect their gameplay.

Choosing José Bonifacio to revolt grants Legendary Native Warriors and ships 20 Tupi Blackwood Archers as well.