The ancient Greeks were some of the first people to have a go at science. The earlier civilizations thought the world was ruled by gods (often bad-tempered and unpredictable and had to be humoured). The ancient Greeks believed that the Universe was governed by rules that humans could understand. This is the basis of science.
These ancient Greeks were not called scientists at that time. They thought and argued about how the world worked, but they did not test things out by doing experiments.
Here are two very famous names from that time:
Plato (427-347 B.C. ), lived in ancient Greece about 2500 years ago. He thought a lot about how the world worked. He did not make observations or do tests.
Aristotle (about 384-322 B.C.) really got science started. He was one of the first scientists and made observations about the world and then did some thinking. He also liked poking around rockpools.
Aristotle lived around the same time as Plato, but was about 40 years younger.