Aristotle

Aristotle is considered the father of zoology.

An excerpt from the article 19 facts about Aristotle
After spending time at the court of Hermias of Atarneus, Aristotle left for the island of Lesbos to study its flora and fauna. Instead of just observing animals, Aristotle started dissecting them to get a better understanding of their anatomy. It was a completely new approach toward science.

Aristotle was also the first scholar to classify animals based on various characteristics, such as the environment they occupy.