Humandrill

Humandrill (ヒューマンドリル) are a type of baboon that Roronoa Zoro encounters in Kuraigana Island. They are highly intelligent creatures capable of imitating humans so much that they will mimic any trait they witness. If they were to see peace they would be peaceful creatures; however, seven years ago, they witnessed a war on Kuraigana Island, causing them to learn how to wield weapons and become bloodthirsty warriors.

The humandrills have been a major hindrance to Zoro's attempts to reach the sea. Though formidable, they were eventually defeated by Zoro.

Trivia

 * Their name is a combination of the word "human" (which they imitate) and Mandrills, a type of monkey they appear to be.